Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The photoelectric converter includes a substrate; and multiple cells
located on the substrate so as to be overlaid. The first cell contacted
with the substrate includes a transparent electrode located on the
substrate, and a first photoelectric conversion layer located on the
transparent electrode. The other cell or each of the others of the
multiple cells includes a porous electroconductive layer located closer
to the substrate and including an electroconductive material, and a
photoelectric conversion layer located on the porous electroconductive
layer. Each of the photoelectric conversion layers of the multiple cells
includes an electron transport layer including an electron transport
material, a dye connected with or adsorbed on the electron transport
material, and a hole transport material. The hole transport material is
also contained in voids of the porous electroconductive layer.

Claims:

1. A photoelectric converter comprising: a substrate; and multiple cells
located on the substrate so as to be overlaid, wherein a first cell
contacted with the substrate includes: a transparent electrode located on
the substrate; and a first photoelectric conversion layer located on the
transparent electrode, and the other of the multiple cells or each of the
others of the multiple cells includes: a porous electroconductive layer
including an electroconductive material while having voids containing a
hole transport material; and a photoelectric conversion layer located on
the porous electroconductive layer so as to be farther from the substrate
than the porous electroconductive layer, and wherein each of the
photoelectric conversion layers of the multiple cells includes: an
electron transport layer including an electron transport material, a dye
connected with or adsorbed on the electron transport material, and the
hole transport material.

2. The photoelectric converter according to claim 1, wherein the dyes
included in the multiple cells have different wavelengths of maximum
absorption.

3. The photoelectric converter according to claim 2, wherein the dye
included in one of the multiple cells has a shorter wavelength of maximum
absorption as the cell becomes closer to the substrate.

4. The photoelectric converter according to claim 1, wherein the dyes
included in the multiple cells have a same wavelength of absorption
maximum.

5. The photoelectric converter according to claim 1, further comprising:
an insulating layer, wherein in any two adjacent cells of the multiple
cells, the electron transport layer of one of the adjacent two cells is
separated from the porous electroconductive layer of the adjacent cell by
the insulating layer, wherein a total thickness of the insulating layer
and the porous electroconductive layer is less than a thickness of the
electron transport layer.

6. The photoelectric converter according to claim 5, wherein the
insulating layer includes a sulfide or an oxide, and is prepared by a
vacuum film forming method.

7. The photoelectric converter according to claim 6, wherein the
insulating layer includes ZnS.

8. The photoelectric converter according to claim 1, wherein the electron
transport material includes an oxide semiconductor.

9. The photoelectric converter according to claim 8, wherein the oxide
semiconductor includes at least one of Ti, Zn and Sn.

10. The photoelectric converter according to claim 1, wherein the
electroconductive material includes at least one of In, Al and Sn.

11. The photoelectric converter according to claim 1, wherein each of the
multiple cells has an inlet from which a liquid can be injected into the
cell.

12. The photoelectric converter according to claim 1, wherein the first
photoelectric conversion layer further includes: an insulating layer
including particulate SiO2, wherein the electron transport layer of
the first photoelectric conversion layer includes dyed TiO2, wherein
the electron transport layer, the insulating layer, and the
electroconductive layer are overlaid on the transparent electrode in this
order, and wherein the electron transport layer of a second photoelectric
conversion layer adjacent to the first photoelectric conversion layer
includes dyed TiO2, and is located on the electroconductive layer of
the first photoelectric conversion layer.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is based on and claims priority pursuant to
35 U.S.C. §119 to Japanese Patent Application No. 2010-261429, filed
on Nov. 24, 2010, in the Japan Patent Office, the entire disclosure of
which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This disclosure relates to a photoelectric converter. Particularly,
this disclosure relates to a layered photoelectric converter, which is
layered using an electrode capable of transmitting a hole.

BACKGROUND OF THE INVENTION

[0003] There are several types of solar cells, but almost all the
commercialized solar cells are diode type solar cells in which silicone
semiconductors are connected. Since these solar cells have high
manufacturing costs at the present time, the solar cells are not broadly
used.

[0004] In attempting to reduce costs of solar cells, Mr. Graetzel of EPL
Lausanne in Switzerland et al. propose a dye-sensitized solar cell with a
high efficiency as described in a Japanese patent No. 2,664,194, and
Nature, 353, pp. 737-740. In addition, Mr. Hara et al. present a paper,
"Electron Transport in Coumarin-Dye-Sensitized Nanocrystalline TiO2
Electrodes" in Journal of Physical Chemistry B, 109, pp. 23776-23778.
There is a desire for commercialization of these dye-sensitized solar
cells.

[0005] The solar cell of Graetzel has a transparent electroconductive
glass substrate, and a porous metal oxide semiconductor layer, a dye
layer adsorbed n the semiconductor layer, an electrolyte layer having a
redox pair, and an opposite electrode. In this solar cell of Graetzel,
the photoelectric conversion efficiency is enhanced by increasing the
surface area of the semiconductor electrode using a porous titanium oxide
as the metal oxide, and by subjecting a dye (ruthenium complex) to a
monomolecular adsorption on the metal oxide semiconductor layer.

[0006] These solar cells are classified into dye-sensitized solar cells
(DSSC), which form one category of batteries. Specific examples of the
photosensitizing dyes for use in such DSSC include materials capable of
absorbing visible light such as bipyridine complexes, terpyridine
complexes, merocyanine dyes, porphyrin, and phthalocyanine.

[0007] It has been considered that it is preferable to use only one dye
having a high purity for a DSSC in order to enhance the photoelectric
conversion efficiency. The reason therefor is considered as follows.
Specifically, when plural kinds of dyes are present on a semiconductor
layer while mixed, exchange of electrons between the dyes or
recombination of electrons and holes is caused, or electrons transferred
from a dye to the semiconductor layer are caught by another dye, and
thereby the number of electrons sent from the exited photosensitizing dye
to the transparent electrode is decreased, resulting in serious decrease
of the quantum yield (i.e., a ratio of generated current to absorbed
photoelectrons). This is disclosed in the paper of Hara, or papers,
"Electron transport process in a dye-sensitized nanocrystalline TiO2
on which both a ruthenium bipyridine complex and a ruthenium biquinoline
complex are adsorbed" by Yanagida et al. in Photochemistry discussion
2005, 2P132, and "Theoretical efficiency of dye-sensitized solar cell" by
Uchida in FAQ at http://kuroppe.tangen.tohoku.ac.jp/ dsc/cell.html.

[0008] Suitable dyes for use alone in such dye-sensitized solar cells
include bipyridine complexes such as
cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylic
acid)ruthenium (II) di-tetrabutyl ammonium complex (i.e., N719). Other
bipyridine complexes such as
cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylic
acid)ruthenium (II) (i.e., N3), and terpyridine complexes such as
tris(isthiocyanato)(2,2':6',2''-terpyridyl-4,4-dicarboxylic
acid)ruthenium (II) tri-tetrabutyl ammonium complex (i.e., Black Dye) can
also be used as the dye.

[0009] When N3 or Black Dye is used, a coadsorbent can be used. Such a
coadsorbent is added to prevent the molecules of a dye from causing
association on a semiconductor layer. Specific examples thereof include
chenodeoxycholic acid, taurodeoxycholic acid, 1-decrylphosphoric acid,
and the like. These coadsorbents have a characteristic such that the
molecules thereof have a functional group, which can be easily adsorbed
on titanium dioxide constituting the semiconductor layer, such as
carboxyl and phosphono groups, while having a sigma bond so as to
intervene between molecules of a dye to prevent interference of the dye
molecules.

[0010] In attempting to efficiently absorb (utilize) incident light and
convert the absorbed light to electric energy, a DSSC is proposed which
includes a first anode including a first sensitizing dye, and a second
anode including a second sensitizing dye located in the vicinity of the
first anode while separated therefrom. By using two kinds of dyes having
different absorption wavelengths for the first and second sensitizing
dyes, it is possible to enhance the conversion efficiency. However, the
DSSC has a drawback in that light is absorbed by an intermediate
electrode, and therefore the second layer insufficiently generates
electricity.

[0011] On the other hand, there is a proposal for an electrochromic device
(EC) using an intermediate electrode. The difference between the EC and
the photoelectric converter of this disclosure will be described later.

[0012] For these reasons, the inventors recognized that there is a need
for a DSSC having a better photoelectric conversion efficiency.

BRIEF SUMMARY OF THE INVENTION

[0013] As an aspect of this disclosure, a photoelectric converter is
provided which includes a substrate, and multiple cells located on the
substrate so as to be overlaid. The first cell contacted with the
substrate includes a transparent electrode located on the substrate, and
a first photoelectric conversion layer located on the transparent
electrode. The other cell or each of the others of the multiple cells
includes a porous electroconductive layer located closer to the substrate
and including an electroconductive material, and a photoelectric
conversion layer located on the porous electroconductive layer. Each of
the photoelectric conversion layers of the multiple cells includes an
electron transport layer including an electron transport material, a dye
connected with or adsorbed on the electron transport material, and a hole
transport material. The hole transport material is also contained in
voids of the porous electroconductive layer.

[0014] The aforementioned and other aspects, features and advantages will
become apparent upon consideration of the following description of the
preferred embodiments taken in conjunction with the accompanying
drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015]FIG. 1 is a schematic view roughly illustrating the cross-section
of an example of the photoelectric converter of this disclosure;

[0016]FIG. 2 is a schematic view illustrating in detail the cross-section
of another example of the photoelectric converter of this disclosure;

[0017] FIG. 3 is a photograph showing a first intermediate electrode
(including ITO) of the photoelectric converter illustrated in FIG. 2;

[0018] FIG. 4 is a graph showing relation between photovoltage and
photocurrent density of a photoelectric converter of Example 1;

[0019]FIG. 5 is a graph showing relation between wavelength of light and
IPCE (incident photon to current conversion efficiency) of the
photoelectric converter of Example 1; and

[0020]FIG. 6 is a schematic view for explaining a way to obtain a power
from a photoelectric converter of Example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The photoelectric converter of this disclosure includes a
substrate, and multiple photoelectric conversion cells located on the
substrate so as to be overlaid. A first photoelectric conversion cell
contacted with the substrate includes a transparent electrode located on
the substrate, and a photoelectric conversion layer located on the
transparent electrode. The other cell or each of the other cells includes
an electroconductive layer including an electroconductive material
therein while having voids, and a photoelectric conversion layer located
on the electroconductive layer so as to be farther from the substrate
than the photoelectric conversion layer. Each of the photoelectric
conversion layers includes an electron transport layer including an
electron transport material, a dye connected with or adsorbed on the
electron transport material, and a hole transport material. In addition,
the hole transport material is also contained in the voids of the
electroconductive layer.

[0022] The difference of the photoelectric converter of this disclosure
from the above-mentioned electrochromic device (EC) is the following.

1. Since information displayed in an electrochromic device is observed
with human eyes, the titanium oxide layer has a thickness of about 1
μm to impart good transparency to the device. In contrast, the
thickness of the titanium oxide layer of the photoelectric converter of
this disclosure is not less than 3 μm. 2. An electrolyte is contained
in an electrochromic device, but a hole transport material is contained
in the photoelectric converter of this disclosure. 3. A suspending agent
is used for an electrochromic device so that the electrochromic device
can display a white background, but such a suspending agent is not used
for the photoelectric converter of this disclosure. 4. A photoelectric
conversion dye is not used for an electrochromic device.

[0023] The structure of the layered photoelectric converter of this
disclosure (hereinafter referred to the photoelectric converter) will be
described by reference to drawings.

[0024]FIG. 1 roughly illustrates the cross-section of an example of the
photoelectric converter of this disclosure, and FIG. 2 illustrates in
detail the cross-section of the example of the photoelectric converter.

[0025] Referring to FIG. 2, the photoelectric converter includes a
substrate 1, and an electrode 3 (electron collecting electrode), an
electron transport layer 5, which includes a dense electron transport
layer 6, a granular electron transport layer 7 and a lattice electron
transport layer 15, and a hole transport layer 8, which includes a first
hole transport layer 9 including a polymer or an electrolyte and a second
hole transport layer 10. These layers are overlaid in this order on the
substrate 1. In addition, an intermediate electrode 21 including a second
insulating layer 25, a first insulating layer 24, a second intermediate
electrode 23, and a first intermediate electrode 22, which are overlaid
in this order from the bottom thereof, is located on the hole transport
layer 8. Further, another electron transport layer 5-2 having a structure
similar to that of the above-mentioned electron transport layer 5 and
including a dense electron transport layer 6-2, a granular electron
transport layer 7-2 and a lattice electron transport layer 15-2, another
first hole transport layer 9-2 having a structure similar to that of the
above-mentioned hole transport layer 9, and another second hole transport
layer 10-2 having a structure similar to that of the above-mentioned hole
transport layer 10 are overlaid on the intermediate electrode 21.
Furthermore, a metal oxide layer 11, a second electrode 33, and an
opposite substrate 50 are overlaid in this order on the electron
transport layer 5-2 and the first hole transport layer 9-2.

[0026] The photoelectric converter illustrated in FIG. 2 has a two-layer
structure, but the structure of the photoelectric converter of this
disclosure is not limited thereto, and it is possible for the
photoelectric converter to have a three- or more-layer structure such
that one or more of the combination of the intermediate electrode 21, the
electron transport layer 5 and the hole transport layer 8 are overlaid in
this order.

[0027] Initially, the substrate 1 and the electron collecting electrode 3
will be described.

[0028] The electron collecting electrode 3 is not particularly limited as
long as the electrode is made of a transparent electroconductive material
which is transparent to visible light, and any known electrodes for use
in general photoelectric converters and liquid crystal panels can be used
therefor.

[0029] Specific examples of the materials for use as the electroconductive
material include indium tin oxide (ITO), fluorine-doped tin oxide (FTO),
and the like. Among these materials, FTO is preferably used.

[0030] The electron collecting electrode 3 preferably has a thickness of
from 5 nm to 100 μm, and more preferably from 50 nm to 10 μm.

[0031] Since the electron collecting electrode 3 has to have a certain
hardness, it is preferable to provide the electron collecting electrode 3
on the substrate 1 made of a material transparent to visible light.
Specific examples of the material for use in the substrate 1 include
glass plates, transparent plastic plates, transparent plastic films,
crystals of transparent inorganic materials, and the like.

[0032] Any known combination materials in which an electron collecting
electrode and a substrate are united can be used for the photoelectric
converter of this disclosure. Specific examples thereof include
FTO-coated glass plates, ITO-coated glass plates, zinc
oxide/aluminum-coated glass plates, FTO-coated transparent plastic films,
ITO-coated transparent plastic films, and the like.

[0033] In addition, transparent electrodes made of tin oxide or indium
oxide doped with a cation or anion having a valence different from that
of tin or indium, electrodes in which a mesh- or stripe-form metal
electrode capable transmitting visible light is located on a transparent
substrate such as glass plates, and the like electrodes can also be used
for the photoelectric converter of this disclosure. These electrodes can
be used alone or in combination.

[0034] In order to reduce the resistivity of the substrate 1, a metal lead
wire and the like can be used. Specific examples of the metal of the
metal lead wire include aluminum, copper, silver, gold, platinum, nickel
and the like. Such a metal lead wire is typically formed on a substrate
by a method such as vapor deposition, sputtering, and pressing, and then
an ITO or FTO layer is formed thereon.

[0035] Next, the electron transport layer 5 will be described.

[0036] The electron transport layer 5 consisting of a thin semiconductor
layer is formed on the above-mentioned electron collecting electrode 3.
It is preferable for the electron transport layer 5 to have a structure
such that a dense electron transport layer (6) is formed on the electron
collecting electrode 3, a porous (granular) electron transport layer (7)
is formed thereon, and a lattice electron transport layer (15) is formed
thereon.

[0037] The dense electron transport layer 6 is formed to prevent
electrical contact of the electron collecting electrode 3 with the hole
transport layer 8. Therefore, the dense electron transport layer 6 may
have a pinhole, a crack and the like as long as the electron collecting
electrode 3 is not physically contacted with the hole transport layer 8.

[0038] The thickness of the dense electron transport layer 6 is not
particularly limited, and is preferably from 10 nm to 1 μm, and more
preferably from 20 nm to 700 nm.

[0039] The term "dense" of the dense electron transport layer 6 means that
the filling bulk density of a particulate inorganic oxide semiconductor
therein is higher than the filling bulk density of a particulate
semiconductor in the granular (porous) electron transport layer 7.

[0041] The lattice electron transport layer 15, which is formed on the
dense electron transport layer 6, consists of a single layer or multiple
layers. Multi-layer type lattice electron transport layers can be
prepared, for example, by a method in which two or more dispersions
including respective particulate semiconductors having different particle
diameters are coated to overlay two or more layers, a method in which two
or more dispersions including different kinds of semiconductors,
different kinds of resins, and/or different kinds of additives are coated
to overlay two or more layers, or the like method.

[0042] When the thickness of the lattice electron transport layer 15
prepared by a single coating method is less than a predetermined
thickness, it is preferable to use a multiple coating method.

[0043] In general, as the thickness of the electron transport layer
increases, the light capturing rate of the layer per a unit area
increases because the amount of a photosensitizer included therein
increases. However, the diffusion length of electrons injected thereinto
also increase, thereby increasing recombination of charges, resulting in
deterioration of electron transportability. Therefore, the thickness of
the electron transport layer 15 is preferably from 10 nm to 1,000 nm.

[0044] Any known masks can be used for forming the lattice of the lattice
electron transport layer 15. The lattice is preferably formed of squares
with a size of not greater than 1 μm, and more preferably about 20 nm.
It is preferable that an electron transport layer is formed in every two
square portions of the lattice.

[0045] The porous electron transport layer 7 will be described later.

[0046] The semiconductor constituting the dense electron transport layer 6
is not particularly limited, and any known semiconductors can be used
therefor.

[0047] Specific examples thereof include element semiconductors such as
silicon and germanium, compound semiconductors such as metal
chalcogenide, compounds having a perovskite structure, and the like.

[0048] Specific examples of the metal chalcogenide include oxides of
metals such as titanium, tin, zinc, tungsten, zirconium, hafnium,
strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, and
tantalum; sulfides of metals such as cadmium, zinc, lead, silver,
antimony, and bismuth; selenides of metals such as cadmium and lead;
tellurides of metals such as cadmium; and the like.

[0049] Specific examples of other compound semiconductors include
phosphides of metals such as zinc, gallium, indium, and cadmium; gallium
arsenide, copper-indium selenide, copper-indium sulfide, and the like.

[0051] These semiconductors can be used alone or in combination. In
addition, the crystal form of the semiconductor is not particularly
limited, and any crystal forms such as single crystal form, polycrystal
form, and amorphous form can be available.

[0052] Among these semiconductors, oxide semiconductors are preferable,
and titanium oxide, zinc oxide, tin oxide, and niobium oxide are more
preferable.

[0053] Although the particle size of the particulate semiconductor for use
in the dense electron transport layer 6 is not particularly limited, the
average primary particle diameter of the particulate semiconductor is
preferably from 1 nm to 100 nm, and more preferably from 5 nm to 50 nm.

[0054] In addition, a particulate semiconductor having a relatively large
average particle diameter of from 50 nm to 500 nm can be added to the
particulate semiconductor to scatter incident light, thereby enhancing
the photoelectric conversion efficiency

[0055] The method for preparing the electron transport layer is not
particularly limited, and any known methods such as vacuum thin film
forming methods (e.g., sputtering), and wet film forming methods can be
used. In view of manufacturing costs, wet film forming methods are
preferable. For example, a method including dispersing a powder or sol of
a semiconductor in a medium to prepare a paste of the semiconductor, and
then applying the paste on an electron collecting electrode formed on a
substrate using a known coating method such as dip coating, spray
coating, wire bar coating, spin coating, roller coating, blade coating,
and gravure coating, or a known printing method such as relief printing,
offset printing, gravure printing, intaglio printing, rubber plate
printing, and screen printing.

[0056] When a mechanical pulverization method or a method using a mill is
used for preparing the semiconductor dispersion, a method in which at
first a particulate semiconductor is fed in a solvent optionally together
with a resin, and the mixture is dispersed by a dispersing machine such
as mills can be used.

[0058] Specific examples of the solvent used for preparing the dispersion
include water; alcohols such as methanol, ethanol, isopropyl alcohol, and
α-terpineol; ketones such as acetone, methyl ethyl ketone, and
methyl isobutyl ketone; esters such as ethyl formate, ethyl acetate, and
n-butyl acetate; ethers such as diethyl ether, dimethoxy methane,
tetrahydrofuran, dioxyolan, and dioxane; amides such as
N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone;
halogenated hydrocarbons such as dichloromethane, chloroform, bromoform,
methyl iodide, dichloroethane, trichloroethane, trichloroethylene,
chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene,
iodobenzene, and 1-chloronaphthalene; hydrocarbons such as n-pentane,
n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane,
cyclohexadiene, benzene, toluene, o-xylene, m-xylene, p-xylene, ethyl
benzene, and cumene; and the like. These solvents can be used alone or in
combination.

[0059] The thus prepared semiconductor dispersion (or the paste) can
include an additive to prevent agglomeration of the dispersed
semiconductor particles. Suitable materials for use as the additive
include acids such as hydrochloric acid, nitric acid and acetic acid;
surfactants such as polyoxyethylene (10) octylphenyl ether; cheletors
such as acetylacetone, 2-aminoethanol, and ethylenediamine; and the like.

[0060] In addition, a thickener can be added to the dispersion to improve
the film formability of the dispersion. Specific examples thereof include
polymers such as polyethylene glycol and polyvinyl alcohol, cellulose
derivatives such as ethyl cellulose, and the like.

[0061] The thus coated semiconductor dispersion is preferably subjected to
a treatment such as sintering, irradiation of microwaves, electron beams
or laser, and pressing to electrically contact particles of the
semiconductor with each other, to improve the mechanical strength of the
film, and to improve the adhesion of the film to the substrate. These
treatments can be performed alone or in combination.

[0062] When sintering is performed, the temperature is not particularly
limited. However, when the temperature is too high, problems such that
the resistance of the substrate seriously increases, and the substrate is
melted occur. Therefore, the temperature is preferably from 30° C.
to 700° C., and more preferably from 100° C. to 600°
C. The sintering time is not particularly limited, but is preferably from
10 minutes to 10 hours.

[0063] After the sintering treatment, the semiconductor may be subjected
to another treatment such as chemical plating using an aqueous solution
or a water/organic solvent solution of titanium tetrachloride, or an
electrochemical plating using an aqueous solution of titanium
trichloride, to increase the surface area of the particulate
semiconductor and to enhance the efficiency of electron injection from a
photosensitizer to the particulate semiconductor.

[0064] When microwave irradiation is performed, the surface to be
irradiated with microwaves is not particularly limited, namely microwaves
may irradiate the electron transport layer or the backside thereof. The
irradiation time is not also particularly limited, but is preferably not
longer than 1 hour.

[0065] The pressing treatment is preferably performed at a pressure of not
less than 100 kg/cm2, and more preferably not less than 1,000
kg/cm2. The pressing time is not also particularly limited, but is
preferably not longer than 1 hour. In addition, the pressing treatment
may be performed while heating the semiconductor.

[0066] A layer of a particulate semiconductor having a diameter of tens of
nanometers, which is prepared by a sintering method or the like, achieves
a porous state. The particulate semiconductor layer in such a porous
state has a very high surface area, and the surface area is represented
using a roughness factor. The roughness factor is defined as a ratio
(RA/A) of the real area (RA) of the surface of the semiconductor
including the area of inner surfaces of voids of the semiconductor to the
surface area (A) of a particulate semiconductor formed on a substrate.
Therefore, the roughness factor is preferably as large as possible.
However, there is a restriction on the thickness of the electron
transport layer, the semiconductor in the electron transport layer of the
photoelectric converter of this disclosure preferably has a roughness
factor of not less than 20.

[0068] The porous electron transport layer 7 is overlaid on the electron
transport layer mentioned above. The porous electron transport layer 7 is
in a porous state and may be constituted of a single layer or multiple
layers.

[0069] A multi-layer type porous electron transport layer can be prepared,
for example, by a method in which two or more dispersions including
respective particulate semiconductors having different particle diameters
are coated to overlay two or more layers, a method in which two or more
dispersions including different kinds of semiconductors, different kinds
of resins, and/or different kinds of additives are coated to overlay two
or more layers, and the like method.

[0070] When the thickness of the porous electron transport layer 7
prepared by a single-layer coating method is less than a predetermined
thickness, it is preferable to use a multiple-layer coating method.

[0071] In general, as the thickness of the electron transport layer
increases, the light capturing rate of the layer per a unit area
increases because the amount of a photosensitizer included therein
increases. However, the diffusion length of electrons injected thereinto
also increase, thereby increasing recombination of charges, resulting in
deterioration of electron transportability. Therefore, the thickness of
the porous electron transport layer 7 is preferably from 100 nm to 100
μm.

[0072] The semiconductor constituting the porous electron transport layer
7 is not particularly limited, and any known semiconductors can be used
therefor.

[0073] Specific examples thereof include element semiconductors such as
silicon and germanium, compound semiconductors such as metal
chalcogenide, compounds having a perovskite structure, and the like.

[0074] Specific examples of the metal chalcogenide include oxides of
metals such as titanium, tin, zinc, tungsten, zirconium, hafnium,
strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, and
tantalum; sulfides of metals such as cadmium, zinc, lead, silver,
antimony, and bismuth; selenides of metals such as cadmium and lead;
tellurides of metals such as cadmium; and the like.

[0075] Specific examples of other compound semiconductors include
phosphides of metals such as zinc, gallium, indium, and cadmium; gallium
arsenide, copper-indium selenide, copper-indium sulfide, and the like.

[0077] These semiconductors can be used alone or in combination. In
addition, the crystal form of the semiconductor is not particularly
limited, and any crystal forms such as single crystal form, polycrystal
form, and amorphous form can be available.

[0078] Among these semiconductors, oxide semiconductors are preferable,
and titanium oxide, zinc oxide, tin oxide, and niobium oxide are more
preferable.

[0079] The particle size of the particulate semiconductor included in the
porous electron transport layer 7 is not particularly limited, but the
average primary particle diameter of the particulate semiconductor is
preferably from 1 nm to 100 nm, and more preferably from 5 nm to 50 nm.

[0080] In addition, a particulate semiconductor having a relatively large
average particle diameter of from 50 nm to 500 nm can be added to the
particulate semiconductor to scatter incident light, thereby enhancing
the photoelectric conversion efficiency.

[0081] The method for preparing the porous electron transport layer 7 is
not particularly limited, and any known methods such as vacuum thin film
forming methods (e.g., sputtering), and wet film forming methods can be
used. In view of manufacturing costs, wet film forming methods are
preferable. For example, a method including dispersing a powder or sol of
a semiconductor in a medium to prepare a paste of the semiconductor, and
then applying the paste on the dense electron transport layer 6 using a
known coating method such as dip coating, spray coating, wire bar
coating, spin coating, roller coating, blade coating, and gravure
coating, or a known printing method such as relief printing, offset
printing, gravure printing, intaglio printing, rubber plate printing, and
screen printing.

[0082] When a mechanical pulverization method or a method using a mill is
used for preparing the semiconductor dispersion, a method in which at
first a particulate semiconductor is fed in a solvent optionally together
with a resin, and the mixture is dispersed by a dispersing machine such
as mills can be used.

[0084] Specific examples of the solvent used for preparing the dispersion
include water; alcohols such as methanol, ethanol, isopropyl alcohol, and
α-terpineol; ketones such as acetone, methyl ethyl ketone, and
methyl isobutyl ketone; esters such as ethyl formate, ethyl acetate, and
n-butyl acetate; ethers such as diethyl ether, dimethoxy methane,
tetrahydrofuran, dioxyolan, and dioxane; amides such as
N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone;
halogenated hydrocarbons such as dichloromethane, chloroform, bromoform,
methyl iodide, dichloroethane, trichloroethane, trichloroethylene,
chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene,
iodobenzene, and 1-chloronaphthalene; hydrocarbons such as n-pentane,
n-hexane, n-octane, 1,5-hexadiene, cyclohexadiene, cyclohexane,
methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene,
p-xylene, ethyl benzene, and cumene; and the like. These solvents can be
used alone or in combination.

[0085] The thus prepared semiconductor dispersion (or the paste) can
include an additive to prevent agglomeration of the dispersed
semiconductor particles. Suitable materials for use as the additive
include acids such as hydrochloric acid, nitric acid and acetic acid;
surfactants such as polyoxyethylene (10) octylphenyl ether; cheletors
such as acetylacetone, 2-aminoethanol, and ethylenediamine; and the like.

[0086] In addition, a thickener can be added to the dispersion to improve
the film formability of the dispersion. Specific examples thereof include
polymers such as polyethylene glycol and polyvinyl alcohol, cellulose
derivatives such as ethyl cellulose, and the like.

[0087] The thus coated semiconductor dispersion is preferably subjected to
a treatment such as sintering, irradiation of microwaves, electron beams
or laser, and pressing to electrically contact particles of the
semiconductor with each other, to improve the mechanical strength of the
film, and to improve the adhesion of the film to the substrate. These
treatments can be performed alone or in combination.

[0088] When sintering is performed, the temperature is not particularly
limited. However, when the temperature is too high, problems such that
the resistance of the substrate seriously increases, and the substrate is
melted occur. Therefore, the temperature is preferably from 30° C.
to 700° C., and more preferably from 100° C. to 600°
C. The sintering time is not particularly limited, but is preferably from
10 minutes to 10 hours.

[0089] After the sintering treatment, the semiconductor may be subjected
to another treatment such as chemical plating using an aqueous solution
or a water/organic solvent solution of titanium tetrachloride, or an
electrochemical plating using an aqueous solution of titanium
trichloride, to increase the surface area of the particulate
semiconductor and to enhance the efficiency of electron injection from a
photosensitizer to the particulate semiconductor.

[0090] When microwave irradiation is performed, the surface to be
irradiated with microwaves is not particularly limited, namely microwaves
may irradiate the electron transport layer or the backside thereof. The
irradiation time is not also particularly limited, but is preferably not
longer than 1 hour.

[0091] The pressing treatment is preferably performed at a pressure of not
less than 100 kg/cm2, and more preferably not less than 1,000
kg/cm2. The pressing time is not also particularly limited, but is
preferably not longer than 1 hour. In addition, the pressing treatment
may be performed while heating the semiconductor.

[0092] A layer of a particulate semiconductor having a diameter of tens of
nanometers, which is prepared by a sintering method or the like, achieves
a porous state. The particulate semiconductor layer in such a porous
state has a very high surface area, and the surface area is represented
using a roughness factor. The roughness factor is defined as a ratio
(RA/A) of the real area (RA) of the surface of the semiconductor
including the area of inner surfaces of voids of the semiconductor to the
surface area (A) of a particulate semiconductor applied on a substrate.
Therefore, the roughness factor is preferably as large as possible.
However, there is a restriction on the thickness of the porous electron
transport layer, the semiconductor in the electron transport layer of the
photoelectric converter of this disclosure preferably has a roughness
factor of not less than 20.

[0093] In a case where both the dense electron transport layer 6 and the
porous electron transport layer are constituted of TiO2, the layers
can be prepared by using different preparation methods. For example, the
dense electron transport layer can be prepared by spin-coating a coating
liquid having a relatively low viscosity. In contrast, when the porous
electron transport layer is prepared, initially a coating liquid
including at least a semiconductor and a binder is applied by a printing
method to form a film, and the film is heated to evaporate the binder,
thereby forming voids in the film, resulting in formation of a porous
electron transport layer.

[0094] In order to enhance the photoelectric conversion efficiency, it is
preferable to adsorb a photosensitization compound on the surface of the
porous electron transport layer 7. The photosensitization compound is not
particularly limited as long as the compound is optically activated by
exciting light. Specific examples of the materials for use as the
photosensitization compound include the following compounds.

[0095] Metal complex compounds disclosed in a published unexamined
Japanese patent application (Kohyo) No. 07-500630 (corresponding to U.S.
Pat. No. 5,463,057), and published unexamined Japanese patent
applications Nos. 10-233238, 2000-26487, 2000-323191, and 2001-59062.

[0107] In order to adsorb a photosenstization compound on the surface of
the porous electron transport layer 7, a method in which the porous
electron transport layer formed on the electron collecting electrode with
the dense electron transport layer 6 therebetween is dipped into a
solution or dispersion of a photosenstization compound; a method in which
a solution or dispersion of a photosenstization compound is applied on
the surface of the porous electron transport layer; or the like method
can be used.

[0108] Dip coating methods, roller coating methods, air knife coating
methods and the like can be used for the first-mentioned method, and wire
bar coating methods, slide hopper coating methods, extrusion coating
methods, curtain coating methods, spin coating methods, spray coating
methods and the like can be used for the second-mentioned method.

[0109] In addition, it is possible to adsorb a photosenstization compound
on the surface of the porous electron transport layer in a supercritical
fluid.

[0110] When a photosenstization compound is adsorbed on the surface of the
porous electron transport layer, a condensing agent can be used.

[0111] Suitable condensing agents include agents which connect physically
or chemically a photosenstization compound with the surface of an
inorganic material so as to serve as a catalyst; agents which affect
stoichiometrically a photosenstization compound and an inorganic material
to advantageously change the chemical equilibrium; and the like.

[0112] In addition, condensing auxiliaries such as thiols and hydroxyl
compounds can be used.

[0113] Specific examples of the solvent for use in preparing a solution or
dispersion of a photosensitization compound include water; alcohols such
as methanol, ethanol, and isopropyl alcohol; ketones such as acetone,
methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl
formate, ethyl acetate, and n-butyl acetate; ethers such as diethyl
ether, dimethoxy methane, tetrahydrofuran, dioxyolan, and dioxane; amides
such as N,N-dimethylformamide, N,N-dimethylacetamide, and
N-methyl-2-pyrrolidone; halogenated hydrocarbons such as dichloromethane,
chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane,
trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene,
bromobenzene, iodobenzene, and 1-chloronaphthalene; hydrocarbons such as
n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane,
methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene,
p-xylene, ethyl benzene, and cumene; and the like. These solvents can be
used alone or in combination.

[0114] When two or more photosensitization compounds are adsorbed, there
is a case where the compounds cause agglomeration depending on the
properties of the compounds. In order to prevent such agglomeration, a
dissociation agent can be used. Specific examples of such a dissociation
agent include steroid compounds such as cholic acid and chenodeoxycholic
acid, long chain alkylcarboxylic acids, long chain alkylphosphoric acids,
and the like. The added amount of such a dissociation agent is preferably
from 0.01 to 500 parts by weight, and more preferably from 0.1 to 100
parts by weight, per 100 parts by weight of the photosensitization
compound used.

[0115] When a photosensitization compound or a combination of a
photosensitization compound and a dissociation agent is adsorbed on the
surface of the porous electron transport layer, the temperature is
preferably from -50° C. to 200° C. In addition, the
adsorption treatment is preferably performed in a dark place.

[0116] The adsorption treatment is performed while the coating liquid is
allowed to settle or agitated. The agitation is performed by an agitator
such as stirrers, ball mills, paint conditioners, sand mills, attritors,
dispersers, supersonic dispersing machines, and the like.

[0117] The adsorption time is preferably from 5 seconds to 1,000 hours,
more preferably from 10 seconds to 500 hours, and even more preferably
from 1 minute to 150 hours.

[0118] Next, the hole transport layer 8 will be described.

[0119] The hole transport layer 8 has a structure such that different hole
transport layers (i.e., the first hole transport layer 9 and the second
hole transport layer 10) are overlaid. The second hole transport layer
10, which is closer to the second electrode 33, includes a polymer.

[0120] By using a polymer having good film formability, the surface of the
porous electron transport layer can be smoothed, thereby enhancing the
photoelectric conversion efficiency of the photoelectric converter.

[0121] In addition, since it is hard for a polymer included in the second
hole transport layer 10 to penetrate into the porous electron transport
layer 7, the porous electron transport layer can be well covered with the
polymer, thereby producing an effect such that occurrence of short
circuit is prevented when the electrode is formed, resulting in
enhancement of the performance of the resultant photoelectric converter.

[0122] Known hole transport materials can be used for the second hole
transport layer 10 which is closer to the second electrode 33. Specific
examples thereof include oxadiazole compounds disclosed in a published
examined Japanese patent application No. 34-5466, triphenylmethane
compounds disclosed in a published examined Japanese patent application
No. 45-555, pyrazoline compounds disclosed in a published examined
Japanese patent application No. 52-4188, hydrazone compounds disclosed in
a published examined Japanese patent application No. 55-42380, oxadiazole
compounds disclosed in a published unexamined Japanese patent application
No. 56-123544, tetraarylbenzidine compounds disclosed in a published
unexamined Japanese patent application No. 54-58445, and stilbene
compounds disclosed in a published unexamined Japanese patent
applications Nos. 58-65440 and 60-98437.

[0123] Known hole transport polymers can be used for the second hole
transport layer 10. Specific examples thereof include polythiophene
compounds such as poly(3-n-hexylthiophene), poly(3-n-octyloxythiophene),
poly(9,9'-dioctyl-fluorene-co-bithiophene),
poly(3,3'''-didodecyl-quarterthiophene),
poly(3,6-dioctylthieno[3,2-b]thiophene),
poly(2,5-bis(3-decylthiophene-2-yl)thieno[3,2-b]thiophene),
poly(3,4-didecylthiophene-co-thieno[3,2-b]thiophene),
poly(3,6-dioctylthieno[3,2-b]thiophene-co-thieno[3,2-b]thiophene),
poly(3,6-dioctylthieno[3,2-b]thiophene-co-thiophene), and
poly(3,6-dioctylthieno[3,2-b]thiophene-co-bithiophene);
polyvinylenephenylene compounds such as
poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene],
poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene], and
poly[(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene)-co-(4,4'-biphe-
nylene-vinylene); polyfluorene compounds such as
poly(9,9'-didodecylfluorenyl-2,7-diyl),
poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(9,10-anthracene)],
poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(4,4'-biphenylene)],
poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(2-methoxy-5-(2-ethylhex-
yloxy)-1,4-phenylene), and
poly[(9,9-dioctyl-2,7-diyl)-co-(1,4-(2,5-dihexyloxy)benzene)];
polyphenylene compounds such as poly[2,5-d]octyloxy-1,4-phenylene], and
poly[2,5-di(2-ethylhexyloxy)-1,4-phenylene]; polyarylamine compounds such
as poly[(9.9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N'-diphenyl)-N,N'-di(p--
hexylphenyl-1,4-diaminobenzene],
poly[(9.9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N'-bis(4-octyloxyphenyl)be-
nzidine-N,N'-(1,4-diphenylene)],
poly[N,N'-bis(4-octyloxyphenyl)benzidine-N,N'-(1,4-diphenylene)],
poly[(N,N'-bis(4-(2-ethylhexyloxy)phenyl)benzidine-N,N'-(1,4-diphenylene)-
], poly[phenylimino-1,4-phenylenevinylene-2,5-dioctyloxy-1,4-phenyleneviny-
lene-1,4-phenylene,
poly[p-tolylimino-1,4-phenylenevinylene-2,5-di(2-ethylhexyloxy)-1,4-pheny-
lenevinylene-1,4-phenylene], and
poly[4-(2-ethylhexyloxy)phenylimino-1,4-biphenylene]; and polythiadiazole
compounds such as
poly[(9,9-dioctylfluorenyl-2,7-diyl)]alt-co-(1,4-benzo(2,1',3)thiadiazole-
)], and poly[3,4-didecylthiophene-co-(1,4-benzo(2,1',3)thiadiazole)].

[0124] Among these compounds, polythiophene compounds and polyarylamine
compounds are preferable because of having a good combination of carrier
mobility and ionization potential.

[0127] In addition, in order to enhance the electroconductivity of the
hole transport layer, oxidizers capable of changing some of molecules of
a hole transport compound into a radical cation can be included in the
hole transport layer. Specific examples thereof include
tris(4-bromophenyl)aluminum hexachloroantimonate, silver
hexachloroantimonate, and nitrosoniumtetrafluoroborate.

[0128] It is not necessary to oxidize all of molecules of the hole
transport material included in the hole transport layer, and it is
acceptable that some of molecules of the hole transport material are
oxidized. The added oxidizer may be included in the hole transport layer
or removed therefrom.

[0129] The hole transport layer 8 is formed on the electron transport
layer 7, which bears a photosensitization compound and which is covered
with a photosensitization compound layer, so as to cover the electron
transport layer. By thus forming the hole transport layer 8, the layer is
evenly adsorbed on and connected with the electron transport layer 7. In
this regard, the hole transport layer 8 is physically adsorbed on the
electron transport layer 7 while the photosensitization compound is
chemically adsorbed on the electron transport layer.

[0130] The method for preparing the hole transport layer 8 is not
particularly limited, and any known methods such as vacuum thin film
forming methods (e.g., sputtering), and wet film forming methods can be
used. In view of manufacturing costs, wet film forming methods are
preferable. When a wet film forming method is used, any known coating
methods such as dip coating, spray coating, wire bar coating, spin
coating, roller coating, blade coating, and gravure coating, or any known
printing methods such as relief printing, offset printing, gravure
printing, intaglio printing, rubber plate printing, and screen printing
can be used.

[0131] It is possible to inject a hole transport material using a
supercritical fluid or a subcritical fluid.

[0132] A supercritical fluid is defined as a material which is present as
a noncondensable high density fluid under temperature/pressure conditions
higher than the critical point thereof below which the material can have
both a gas state and a liquid state at the same time. Even when such a
supercritical fluid is pressed, the supercritical fluid is not aggregated
(condensed). Any known supercritical fluids can be used for this
application. Among these supercritical fluids, supercritical fluids
having a low critical temperature and a low critical pressure are
preferably used for this application.

[0133] Specific examples of the materials for use as the supercritical
fluid in this application include carbon monoxide, carbon dioxide,
ammonia, nitrogen, water, alcohols (e.g., methanol, ethanol, and
n-butanol), hydrocarbons (e.g., ethane, propane, 2,3-dimethylbutane,
benzene, and toluene), halogenated hydrocarbons (e.g., methylene
chloride, and chlorotrifluoromethane), ethers (e.g., dimethyl ether), and
the like. These materials can be used alone or in combination. Among
these materials, carbon dioxide is preferably used because of having a
critical temperature (31° C.) near room temperature and a critical
pressure (7.3 MPa) near normal pressure. Therefore, carbon dioxide can be
easily changed to a supercritical state. In addition, carbon dioxide is
highly safe because of being nonflammable. When supercritical carbon
dioxide is present under normal temperature and normal pressure
conditions, it becomes a gas. Therefore, carbon dioxide can be easily
collected and reused.

[0134] A sub-critical fluid is defined as a material which is present as a
high pressure liquid under a temperature/pressure condition in the
vicinity of the critical point of the material. Any known sub-critical
fluids can be used for this application. The materials mentioned above
for use as the supercritical fluids can also be used as sub-critical
fluids.

[0135] The critical temperature and critical pressure are not particularly
limited. The critical temperature is preferably from -273° C. to
300° C. and more preferably from 0° C. to 200° C.

[0136] When the hole transport layer is prepared by using a supercritical
fluid or a sub-critical fluid, an organic solvent or an entrainer can be
added thereto to adjust the solubility of a hole transport material in
the fluid.

[0137] Any known solvents and entrainers can be used. Specific examples
thereof include ketones such as acetone, methyl ethyl ketone, and methyl
isobutyl ketone; esters such as ethyl formate, ethyl acetate, and n-butyl
acetate; ethers such as diisopropyl ether, dimethoxy ethane,
tetrahydrofuran, dioxyolan, and dioxane; amides such as
N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone;
halogenated hydrocarbons such as dichloromethane, chloroform, bromoform,
methyl iodide, dichloroethane, trichloroethane, trichloroethylene,
chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene,
iodobenzene, and 1-chloronaphthalene; hydrocarbons such as n-pentane,
n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane,
cyclohexadiene, benzene, toluene, o-xylene, m-xylene, p-xylene, ethyl
benzene, and cumene; and the like. These solvents can be used alone or in
combination.

[0138] Specific examples of electrolytes for use as the hole transport
material include combination of iodine (I2) and a metal iodide or an
organic iodide; combination of bromine (Br2) and a metal bromide or
an organic bromide; metal complexes such as ferrocyanic acid
salt-ferricyanic acid salt, and ferrocene-ferricinium ion; sulfur
compounds such as sodium polysulfide, and alkylthiol-alkyldisulfide;
viologen dyes, hydroquinone-quinine; and the like.

[0139] Specific examples of the metal of the metal compounds mentioned
above include Li, Na, K, Mg, Ca and Cs, but are not limited thereto.
Specific examples of the cation of the organic compounds mentioned above
include cations of quaternary ammoniums such as tetraalkylammoniums,
pyridiniums, and imidazoliums, but are not limited thereto. These metals
and cations can be used alone or in combination.

[0140] Among these electrolytes, combinations of I2 and LiI, and
combinations of NaI and a quaternary ammonium compound such as
imidazolium iodide are preferably used.

[0141] When an electrolyte is used while dissolved in a solvent, the
concentration of the electrolyte in the solution is preferably from 0.05M
to 10M, and more preferably from 0.2M to 3M. The concentration of I2
or Br2 is preferably from 0.0005M to 1M, and more preferably from
0.001M to 0.5M.

[0142] In addition, in order to enhance the properties of the
photoelectric converter such as open-circuit voltage and short-circuit
current, additives such as 4-tert-butylpyridine and benzimidazolium can
be added to the electrolyte.

[0143] Specific examples of the solvent constituting the electrolyte
include water, alcohols, ethers, esters, carbonates, lactones,
carboxylates, phosphoric trimesters, heterocyclic compounds, nitriles,
ketones, amides, nitromethane, halogenated hydrocarbons,
dimethylsulfoxide, sulfolane, N-methylpyrrolidone,
1,3-dimethylimidazolidinone, 3-methyloxazolidine, and hydrocarbons, but
are not limited thereto. These materials can be used alone or in
combination. In addition, ionic liquids (at room temperature) such as
quaternary ammonium salts of tetraalkyls, pyridiniums, and imidazolium
can also be used as the solvent.

[0144] Next, the metal oxide layer 11 will be described.

[0145] The metal oxide layer 11 is optionally formed between the hole
transport layer 9-2 and the second electrode 33. Specific examples of the
metal oxide constituting the metal oxide layer 11 include molybdenum
oxide, tungsten oxide, vanadium oxide, and nickel oxide. Among these
metal oxides, molybdenum oxide is preferable.

[0146] The method for preparing the metal oxide layer 11 is not
particularly limited, and any known methods such as vacuum thin film
forming methods (e.g., sputtering), and wet film forming methods can be
used. In view of manufacturing costs, wet film forming methods are
preferable. For example, a method including dispersing a powder or sol of
a metal oxide in a medium to prepare a paste of the metal oxide, and then
applying the paste on the hole transport layer using a known coating
method such as dip coating, spray coating, wire bar coating, spin
coating, roller coating, blade coating, and gravure coating, or a known
printing method such as relief printing, offset printing, gravure
printing, intaglio printing, rubber plate printing, and screen printing.

[0147] The thickness of the metal oxide layer 11 is preferably from 0.1 nm
to 50 nm, and more preferably from 1 nm to 10 nm.

[0148] Next, the second electrode 33 will be described.

[0149] The second electrode 33, which serves as a hole collecting
electrode, is formed on the hole transport layer 9-2 or the metal oxide
layer 11.

[0150] The material mentioned above for use in the electron collecting
electrode 3 can also be used for the second electrode 33. If the second
electrode 33 has sufficient strength and sealing ability, a substrate
supporting the second electrode is not necessarily used.

[0151] Specific examples of the materials for use in the second electrode
33 include metals such as platinum, gold, silver, copper, and aluminum,
carbon compounds such as graphite, fullerene, and carbon nanotube,
electroconductive metal oxides such as ITO and FTO, and electroconductive
polymers such as polythiophene, and polyaniline. These materials can be
used alone or in combination.

[0152] The thickness of the second electrode 33 is not particularly
limited.

[0153] The method for preparing the second electrode 33 is determined
depending on the materials used for the second electrode and the lower
layer (such as hole transport layer 9-2), and methods such as coating,
laminating, vapor deposition, and CVD can be used.

[0154] In order that this example can serve as a photoelectric converter,
at least one of the first electrode (electron collecting electrode) 3 and
the second electrode (hole collecting electrode) 33 has to be
substantially transparent.

[0155] It is preferable for this example of the photoelectric converter of
this disclosure that the first electrode 3 is transparent and light
enters from the first electrode side. In this case, it is preferable to
use a material capable of reflecting light for the second electrode 33.
Specific examples of the light reflecting material include glass or
plastics on which a metal layer or an electroconductive oxide layer is
formed by evaporation, metal thin films, and the like.

[0156] In addition, it is preferable to form an antireflection layer is
formed on the side of the photoelectric converter from which light
enters.

[0157] An object of this disclosure is to provide a polylinker by which a
thin solar cell can be produced at a relatively low temperature.
Specifically, by using such a polylinker, a solar cell can be formed on a
flexible substrate, which is made of a material sensitive to heat such as
polymers.

[0158] In addition, another object of this disclosure is to provide a
solar cell which can be easily prepared by a continuous preparation
method, and a method for preparing a solar cell. For example, a
roll-to-roll method can be used for preparing a solar cell instead of
conventional batch methods. Specifically, this disclosure provides a
method in which nano-sized particles of a metal oxide in a DSSC can be
connected with each other by a polylinker without heating or by heating
at a relatively low temperature. For example, by contacting nano-sized
metal oxide particles with a polylinker, which is dispersed in a solvent
such as n-butanol, at room temperature or a temperature lower than
300° C., the nano-sized particles can be connected with each
other.

[0159] In this disclosure, an electrolyte composition is provided, and a
method for preparing a solid or solid-like electrolyte is also provided.
In this regard, the electrolyte composition, the solid electrolyte and
the solid-like electrolyte correspond to the hole transport material
mentioned above.

[0160] Replacing a liquid electrolyte with a solid or solid-like
electrolyte makes it possible to prepare a flexible solar cell using a
continuous preparation method such as roll-to-roll methods and web
methods. In addition, gel electrolytes also solve the electrolyte leaking
problem, thereby imparting good durability to DSSC. Further, this
disclosure provides a method or a material for allowing a liquid
electrolyte to gelate at room temperature or a relatively low temperature
of lower than 300° C., thereby making it possible to produce a
flexible solar cell at a relatively low temperature.

[0161] The gel electrolyte for use in this disclosure includes a
redox-active component, and a polymer or a non-polymer with a small
amount of plural ligands, which has been allowed to gelate by a metal ion
complex forming method. In addition, an organic compound capable of
forming a complex with a metal ion at multiple sites (for example, due to
presence of a bound group) can be preferably used. In this regard, the
redox-active component may be a liquid or a solid dissolved in a liquid
solvent. The bound group represents a group including at least one donor
atom having a high electron density such as O, N, S and P(III). The
multiple bound groups can be present in a side chain or a main chain of
the polymer or non-polymer. Alternatively, the bound groups can be
present as a part of a dendrimer or a starburst compound.

[0162] By incorporating a metal ion (particularly lithium ion) into a
liquid inorganic electrolyte composition, the properties of the
photoelectric converter (solar cell) such as photocurrent, and
open-circuit voltage can be improved, thereby enhancing the conversion
efficiency of the solar cell.

[0163] In addition, this disclosure also provides a method for
incorporating an electrolyte, a gelation compound, and a compound
including a gel electrolyte and lithium in a solar cell.

[0164] This disclosure provides a composition and a method for
satisfactorily adhering a solar cell to a substrate even at a relatively
low temperature of lower than 300° C. By using such a composition
or a method, a flexible thin solar cell can be produced at low costs
using a continuous preparation method.

[0165] This disclosure also provides an oxide semiconductor coating liquid
which includes an oxide semiconductor such as nano-sized dyed metal oxide
particles and which can be applied on a flexible and transparent
substrate at room temperature. Specifically, a nano-sized titania is
provided which has a good mechanical stability and which can be
satisfactorily adhered to a flexible and transparent substrate or a
surface of a substrate, on which an electroconductive material layer is
formed, even after the coated liquid is dried at a temperature of from
about 50° C. to about 150° C. By using such a titania, a
flexible thin solar cell can be produced by a continuous preparation
method.

[0166] This disclosure also provides a co-sensitizer capable of enhancing
the performance of a sensitizing dye. Such a co-sensitizer is adsorbed on
the surface of nano-sized oxide semiconductor particles, which are
connected with each other, together with a sensitizing dye. Such a
co-sensitizer reduces chance of reverse transportation of electrons from
the nano-sized oxide semiconductor particles to the sensitizing dye,
thereby enhancing the conversion efficiency of the solar cell by about
17%. The co-sensitizer is a material which includes an aromatic amine
compound, a carbazole compound, or a compound having a condensed ring and
which has an ability of donating electrons to an acceptor while stably
forming a cation radical.

[0167] Thus, this disclosure provides a method for connecting nano-sized
particles with each other at a relatively low temperature, which includes
preparing a solution including a solvent and a polylinker, and contacting
nano-sized metal oxide particles with the solution at a relatively low
temperature of lower than about 300° C., preferably lower than
200° C., more preferably lower than 200° C., and even more
preferably room temperature. In this regard, the solution includes the
polylinker in an amount sufficient for connecting at least part of the
nano-sized metal oxide particles. The polylinker preferably includes a
large molecule having a long chain, which preferably has substantially
the same structure as the nano-sized metal oxide particles in the main
chain thereof and which has at least one reactive group in the main
chain. The nano-sized metal oxide particles preferably have a formula
MxOy, wherein each of x and y represents an integer. Specific examples of
the metal M include Ti, Zr, W, Nb, Ta, Tb, Mo and Sn.

[0168] The polylinker is preferably poly(n-butyltitanate), and the solvent
is preferably n-butanol.

[0169] The mechanism of connecting at least part of nano-sized metal oxide
particles is a physical or electrical bridge formed by at least one
reactive group connected with the metal oxide particles. The metal oxide
particles are preferably arranged as a thin film on a substrate, for
example, by a dipping method in which a substrate is dipped into a
solution including metal oxide particles and a polylinker, a spraying
method in which a solution including metal oxide particles and a
polylinker is sprayed on a substrate, or a coating method in which a
solution including metal oxide particles and a polylinker is applied on a
substrate. Alternatively, a method in which nano-sized metal oxide
particles are applied on a substrate and then a solution including a
polylinker is applied thereon can also be used.

[0170] In addition, the preparation method can include a step of
contacting nano-sized metal oxide particles with a modifying solution.

[0172] The present invention provides a polylinker solution including (1)
a polylinker having a formula --[O-M(OR)i-]m-, (2) nano-sized metal oxide
particles having a formula MxOy, and (3) a solvent, wherein each of i, m,
x, and y is a positive integer, M represents Ti, Zr, Sn, W, Nb, Ta, Mo or
Tb, R represents an alkyl group, an alkenyl group, an alkynyl group, an
aromatic group, or an acyl group.

[0173] The polylinker solution preferably includes the polylinker in an
amount sufficient for connecting at least part of nano-sized metal oxide
particles with each other at a temperature of lower than 300° C.,
and preferably lower than 100° C. The polylinker solution is
preferably a 1 wt % n-butanol solution of poly(n-butyltitanate).

[0174] Another example of the photoelectric converter is a flexible solar
cell in which nano-sized particles of a photosensitive material, which
are connected with each other, and an electron transport material are
sandwiched by first and second flexible and transparent substrates. The
nano-sized photosensitive material particles are preferably connected
with each other by a polylinker. The average particle diameter of the
nano-sized photosensitive material particles is preferably from about 5
nm to about 80 nm. The nano-sized photosensitive material is preferably
titanium dioxide, zirconium oxide, zinc oxide, tungsten oxide, niobium
oxide, lanthanum oxide, tantalum oxide, tin oxide, terbium oxide, or a
combination of two or more of these metal oxides. The nano-sized
photosensitive material can include a photosensitive agent (dye) such as
xanthine, cyanine, merocyanine, phthalocyanine, and pyrrole. The
photosensitive agent can include a metal ion such as divalent or
trivalent metal ions. In addition, the photosensitive agent can include a
transition metal complex such as ruthenium complexes, osmium complexes,
and iron complexes. The electron transport material is preferably a
polymer electrolyte. This electron transport material has a light
transmission of not less than about 60%.

[0175] At least one of the first and second flexible substrates includes a
transparent substrate such as polyethylene terephthalate and polyethylene
naphthalate. The flexible solar cell can have a layer having a catalytic
activity between the first and second flexible substrates. In addition,
the flexible solar cell can have a layer of an electroconductive material
(such as indium tin oxide) located on at least one of the first and
second flexible substrates.

[0176] This disclosure provides an electrolyte composition suitable for
solar cells. The electrolyte includes a metal ion, and an organic
compound capable of forming a complex with the metal ion at plural sites.
The metal ion is preferably a lithium ion. Specific examples of the
organic compound include poly(4-vinylpyridine), poly(2-vinylpyridine),
polyethylene oxide, polyurethane, polyamide, and the like. These
materials can be used alone or in combination. The electrolyte
composition can include a gelation compound such as lithium salts having
a formula LiX, wherein X represents an anion such as a halogen atom, a
perchlorate group, a thiocyanate group, a trifluoromethylsulfonate group,
and a hexafluorophosphate group. In addition, the electrolyte composition
can include iodine at a concentration of about 0.05M.

[0177] This disclosure provides an electrolyte solution for use in
preparing a solar cell. The electrolyte solution includes a compound
having a formula MiXj, wherein each of i and j is a positive integer, X
represents a monovalent or polyvalent anion such as a halogen atom, a
perchlorate group, a thiocyanate group, a trifluoromethylsulfonate group,
a hexafluorophosphate group, a sulfate group, a carbonate group, or a
phosphate group, and M represents a monovalent or polyvalent metal cation
such as Li, Cu, Ba, Zn, Ni, lanthanide metals, Co, Ca, Al, and Mg.

[0178] This disclosure also provides a solar cell in which nano-sized
particles of a photosensitive material, which are connected with each
other, and an electrolyte redox system are sandwiched by first and second
light transmissive substrates. The electrolyte redox system preferably
includes a gelation compound including a metal ion, a polymer capable of
forming a complex with the metal ion at plural sites, and an electrolyte
solution. The metal ion is preferably a lithium ion, and the electrolyte
solution includes an ionic liquid including an imidazolium iodide based
compound including iodine at a concentration of 0.05M, and a deactivating
agent such as t-butylpyridine, methylbenzimidazole, or chemical species
which have a pair of free electrons and which can be adsorbed on titania.

[0179] This disclosure provides a method for allowing an electrolyte
solution to gelate, which can be used for preparing a DSSC. The method
includes preparing an electrolyte solution, and adding a material capable
of forming a complex at plural sites, and a metal ion capable of forming
the complex at the sites to the electrolyte solution. The above-mentioned
steps are performed at a temperature of lower than 50° C. and a
normal pressure. The metal ion is preferably a lithium ion. The gelation
speed can be controlled by changing the concentration of a counter ion in
the electrolyte. In addition, by changing the anion, the gelation speed
and gelation rate can be controlled. For example, even when the
concentration of lithium ion is constant, an iodide can allow an
electrolyte solution to gelate at a higher gelation rate than that in a
case of using a chloride or thiocyanic acid.

[0180] In addition, this disclosure provides a method for reducing
transfer of electrons to chemical species in the electrolyte in the solar
cell of this disclosure. The method includes providing a solar cell
portion including a sensitizing dye layer, providing an electrolyte
solution including a compound capable of forming a complex at plural
sites, and adding a compound MX in an amount sufficient for allowing the
electrolyte solution to gelate, wherein M represents an alkali metal, and
X represents an anion such as a halogenide group, a perchlorate group, a
thiocyanate group, a trifluoromethylsulfonate group, a
hexafluorophosphate group, and then incorporating the thus prepared gel
electrolyte into the solar cell portion.

[0181] This disclosure also provides an electrolyte composition suitable
for solar cells. The electrolyte composition includes an ionic liquid,
which includes imidazolium iodide, in an amount of about 90% by weight,
water in an amount of from 0 to 10% by weight, iodine at a concentration
of 0.05M, and methylbenzimidazole. The imidazolium iodide based ionic
liquid preferably includes butylmethylimidazolium iodide,
propylmethylimidazolium iodide, hexylmethylimidazolium iodide, or a
combination of two or more of these iodides. The electrolyte composition
can include LiCl. The amount of LiCl is preferably from about 1% by
weight to about 6% by weight. The electrolyte composition can include
LiI. The amount of LiI is preferably from about 1% by weight to about 6%
by weight.

[0182] This disclosure provides a method for forming a layer of a
nano-sized semiconductor oxide on a substrate. The method includes
providing a substrate, coating a surface of a substrate with a primer
including a semiconductor oxide, and coating the primer layer with a
suspension of a nano-sized semiconductor oxide at a temperature of lower
than 300° C., preferably lower than 150° C., and more
preferably room temperature. The primer layer is formed to improve
adhesion of the nano-sized semiconductor oxide to the substrate. The
primer layer can be a film of a semiconductor oxide (such as titanium
dioxide) formed by a vacuum coating method. The primer layer can be a
layer of a particulate semiconductor oxide including titanium dioxide or
tin oxide. The primer layer can include a thin layer including a
polylinker solution, wherein the polylinker is preferably a poly(titanium
(IV) butoxide) or a macromolecule having a long chain. The substrate is
preferably made of a flexible and light transmissive material. In
addition, electroconductive materials such as indium tin oxide can be
used for the substrate. Alternatively, flexible and light transmissive
materials on which an electroconductive material layer is formed can be
used for the substrate.

[0183] This disclosure also provides a solar cell including a first
flexible and light transmissive substrate, a primer layer located on the
substrate, a nano-sized photosensitive material layer which includes a
suspension of nano-sized semiconductor oxide connected with each other
and which is located on the primer layer, a charge transport material
layer, and a second flexible and light transmissive substrate, wherein
these layers are sandwiched by the first and second substrates. Specific
examples of the nano-sized photosensitive material include titanium
oxide, zirconium oxide, zinc oxide, tungsten oxide, niobium oxide,
lanthanum oxide, tin oxide, terbium oxide, tantalum oxide, and a
combination of two or more of these metal oxides. The primer layer can be
a film of a semiconductor oxide (such as titanium dioxide) formed by a
vacuum coating method. The primer layer can be a layer of a particulate
semiconductor oxide including titanium dioxide or tin oxide. The primer
layer can include a thin layer including a polylinker solution, wherein
the polylinker is preferably a poly(titanium (IV) butoxide) or a
macromolecule having a long chain. A layer of an electroconductive
material such as indium tin oxide can be formed on the first substrate.

[0184] This disclosure provides a coating liquid for use in preparing a
layer of a solar cell. The coating liquid includes a solvent, a
nano-sized particulate material dispersed in the solvent, a polymer
binder dissolved in the solvent. When the coating liquid is applied on a
substrate, followed by drying, both the particulate material and the
polymer binder are located on the substrate, thereby forming a nano-sized
particle film having good mechanical stability on the substrate. The film
can be formed at room temperature. The coating liquid can include acetic
acid. In addition, the nano-sized particulate material is preferably
nano-sized titanium oxide. The weight ratio (T/B) of the titanium oxide
(T) to the binder resin (B) is from 0.1/100 to 20/100, and preferably
from 1/100 to 10/100. The solvent includes water and/or an organic
solvent. Specific examples of the polymer binder includes
polyvinylpyrrolidone, polyethylene oxide, hydroxyethyl cellulose, ethyl
cellulose, hydroxypropyl cellulose, and polyvinyl alcohol. In addition,
the coating liquid can include a polylinker connecting the nano-sized
particles with each other. The substrate is preferably made of a flexible
and light transmissive material.

[0185] This disclosure provides a method for forming a layer of the solar
cell. Specifically, the method includes dispersing a nano-sized
particulate material in a solvent, dispersing a polymer binder in the
nano-sized particulate material dispersion to prepare a coating liquid,
and applying the coating liquid on a substrate to form a nano-sized
particle film having good mechanical stability on the substrate. By using
this method, a nano-sized particle film can be formed at room
temperature. The method can further include drying the coated liquid at a
temperature of from about 50° C. to about 150° C.

[0186] This disclosure also provides a flexible solar cell including (1) a
charge transport material layer located between first and second flexible
and light transmissive substrates, and (2) a layer located between the
substrates and prepared by coating a coating liquid, in which a
nano-sized particulate semiconductor oxide is dispersed in a solvent and
a polymer binder is dissolved in the solvent. The nano-sized particulate
material is preferably a nano-sized particulate material connected with
each other by a polylinker. Specific examples of the nano-sized
particulate material include titanium oxide, zirconium oxide, zinc oxide,
tungsten oxide, niobium oxide, lanthanum oxide, tin oxide, terbium oxide,
tantalum oxide, and a combination of two or more of these metal oxides.
The nano-sized particulate material can include a photosensitive agent
(dye) such as xanthine, cyanine, merocyanine, phthalocyanine, and
pyrrole. The photosensitive agent can include a metal ion such as
divalent or trivalent metal ions. In addition, the photosensitive agent
can include a transition metal complex such as ruthenium complexes,
osmium complexes, and iron complexes. The substrate is preferably made of
polyethylene terephthalate. Specific examples of the polymer binder
includes polyvinylpyrrolidone, polyethylene oxide, hydroxyethyl
cellulose, ethyl cellulose, hydroxypropyl cellulose, and polyvinyl
alcohol.

[0187] This disclosure provides a photosensitive material. The
photosensitive material includes a sensitizing dye to accept
electromagnetic energy, and a co-sensitizer having a coordinate bond
group so as to co-adsorb on a surface of a nano-sized metal oxide layer
together with the sensitizing dye. The sensitizing dye is preferably
cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxyrato)-ruthenium
(II). The co-sensitizer preferably includes an aromatic amine or
carbazole. Specific examples thereof include diphenylaminobenzoic acid,
2,6-bis(4-benzoate)-4-(4-N,N'-diphenylamino)phenylpyridinecarboxylic
acid, and N',N-diphenylaminophenylpropionic acid. Specific examples of
the coordinate bond group include carboxyl groups, phosphate groups, and
chelate groups (such as oxime and alfa-ketoenolate). The added amount of
the co-sensitizer is less than about 50% by mol, preferably from about 1%
by mol to about 20% by mol, and more preferably from about 1% by mol to
about 5% by mol, based on the sensitizing dye.

[0188] This disclosure provides a photosensitive nano-sized particulate
material layer for use in a solar cell. The layer include a sensitizing
dye to accept electromagnetic energy, a co-sensitizer having a coordinate
bond group, a nano-sized particulate photosensitive material having a
surface on which the sensitizing dye and the co-sensitizer are to be
co-adsorbed. The nano-sized particulate photosensitive material is
preferably a nano-sized semiconductor oxide.

[0189] This disclosure also provides a method for preparing a
photosensitive nano-sized particulate material layer. The method includes
providing a layer of a nano-sized particulate material in which particles
are connected with each other, applying a sensitizing dye on the
nano-sized particulate material layer, and co-adsorbing a co-sensitizer
having a coordinate bond group on the surface of the nano-sized
particulate material. The photosensitive nano-sized particulate material
is preferably a nano-sized particulate semiconductor oxide.

[0191] The added amount of the co-sensitizer is less than about 50% by
mol, and preferably from about 1% by mol to about 20% by mol, based on
the sensitizing dye.

[0192] This disclosure provides a flexible solar cell including (1) a
nano-sized particulate photosensitive material in which particles thereof
are connected with each other and which includes (i) a sensitizing dye to
accept electromagnetic energy, and (ii) a co-sensitizer having a
coordinate bond group, and (2) a charge transport material. Both the
sensitizing dye and the co-sensitizer are adsorbed on a surface of the
nano-sized particulate photosensitive material. The nano-sized
particulate photosensitive material and the charge transport material are
sandwiched by first and second flexible and light transmissive
substrates. The particles of the nano-sized particulate photosensitive
material are preferably connected with each other by a polylinker. The
average particle diameter of the nano-sized particulate photosensitive
material is preferably from about 10 nm to about 40 nm. Specific examples
of the nano-sized particulate photosensitive material include titanium
oxide, zirconium oxide, zinc oxide, tungsten oxide, niobium oxide,
lanthanum oxide, tin oxide, terbium oxide, tantalum oxide, and a
combination of two or more of these metal oxides. The charge transport
material preferably includes a redox electrolyte or a polymer
electrolyte. The charge transport material preferably has light
transmission of not less than about 60% in visible region.

[0193] At least one of the first and second flexible substrates includes a
transparent substrate such as polyethylene terephthalate and polyethylene
naphthalate. The flexible solar cell can have a layer having a catalytic
activity between the first and second soft substrates. The layer having a
catalytic activity preferably includes platinum. In addition, the
flexible solar cell can have a layer of an electroconductive material
(such as indium tin oxide) located on at least one of the first and
second flexible substrates.

[0194] Next, the photoelectric converter of this disclosure will be
described in detail by reference to examples.

A. Connection of Nano-Sized Particles

[0195] As mentioned above briefly, this disclosure provides a polylinker
which makes it possible to produce a web-form solar cell at a relatively
low sintering temperature (lower than about 300° C.). In general,
the term "sintering" means a process in which a material is heated at a
temperature of not lower than about 400° C. However, in this
application, "sintering" means a process in which nano-sized particles
are connected with each other at any temperature. In addition, this
disclosure also provides a method for connecting nano-sized particles for
use in a solar cell using a polylinker. Further, this disclosure also
provides a low temperature sintering process which makes it possible to
make a solar cell using a flexible polymer substrate. By using a flexible
substrate, continuous manufacturing methods such as roll-to-roll and web
methods can be used for preparing solar cells.

[0196] In this disclosure, the polylinker is used together with a
nano-sized particulate material having a formula MxOy, wherein M
represents Ti, Zr, W, Nb, La, Ta, Tb, or Sn, and each of x and y is a
positive integer.

[0197] The polylinker has a chain similar to the structure of the
nano-sized particulate metal oxide used while having a reactive group
having a formula (OR)i, wherein R represents a hydrogen atom, an acetate
group, an alkyl group, an alkenyl group, an alkynyl group, an aromatic
group, or an acyl group, and i is a positive integer. Specific examples
of the alkyl groups include ethyl, propyl, butyl and pentyl groups, but
are not limited thereto. Specific examples of the alkenyl groups include
ethenyl, propenyl, butenyl, and pentenyl groups, but are not limited
thereto. Specific examples of the alkynyl groups include ethynyl,
propynyl, butynyl, and pentynyl groups, but are not limited thereto.
Specific examples of the aromatic groups include phenyl, and benzyl
groups, but are not limited thereto. Specific examples of the acyl groups
include acetyl and benzoyl groups, but are not limited thereto. In
addition, a halogen atom such as chlorine, bromine and iodine atoms can
be used instead of the reactive group (OR)i.

[0198] The polylinker preferably has a branched chain including two chains
each having a formula -M-O-M-O-M-O-- and reactive groups having formulae
(OR)i and (OR)i+1, wherein R represents one of the atom or groups
mentioned above, and i is a positive integer. The two chains have
structures similar to the structure of the nano-sized particulate metal
oxide used. Specifically, the polylinker has a structure having a formula
-M(OR)i-O-(M(OR)i-O)n-M(OR)i+1-, wherein each of i and n is a positive
integer.

[0199] A polylinker, which is a low concentration solution of only one
polylinker, can crosslink a large number of nano-sized particles, thereby
forming a network of the nano-sized particles. However, when the
concentration of the polylinker solution is increased, the nano-sized
particles are coated with the polylinker polymer. Since the polylinker
polymer is flexible, the nano-sized particles thus coated with the
polylinker polymer can form a thin film. Since the electric properties
and structural properties of the polylinker polymer are similar to those
of the nano-sized particles, the electric properties of the nano-sized
particles coated with the polylinker polymer are substantially the same
as those of the nano-sized particles themselves.

[0200] In this disclosure, flexible materials having a light transmission
of not less than about 60% in visible region are preferably used for the
substrate. Specific examples of the materials include polyethylene
terephthalate (PET), polyimide, polyethylene naphthalate (PEN),
polymer-like hydrocarbons, cellulose compounds, and combinations of these
materials. A surface of PET and PEN can have a layer including one or
more electroconductive metal oxides such as indium tin oxide (ITO),
fluorine-doped tin oxide, tin oxide, and zinc oxide.

[0201] By using such a polylinker, nano-sized particles can be connected
with each other at a relatively low temperature of much lower than
400° C., and generally less than about 300° C.

[0202] By performing the treatment at a temperature in the temperature
range, materials, which are damaged at a temperature in a conventional
high treatment temperature range, can be used for the flexible substrate.
In this disclosure, nano-sized particles can be connected with each other
at a temperature of lower than 300° C., or a temperature of lower
than 100° C. Further, it is possible to perform the treatment
using a polylinker at room temperature of from about 18° C. to
30° C. and normal pressure of about 760 mmHg.

[0203] The reactive group of the polylinker is connected with the
substrate, the coated layer of the substrate, or the oxide layer of the
substrate used by a covalent bond, an ionic bond and/or a hydrogen bond.
Since the polylinker is reacted with the oxide layer on the substrate,
the oxide layer (i.e., nano-sized particles) can be connected with the
substrate via the polylinker.

[0204] In the photoelectric converter of this disclosure, nano-sized metal
oxide particles are contacted with a polylinker dispersed or dissolved in
a proper solvent at room temperature or below room temperature, or at a
relatively high temperature of not higher than 300° C., so that
the nano-sized metal oxide particles are connected with each other. The
method of contacting the nano-sized metal oxide particles with the
polylinker solution is not particularly limited, and any know methods can
be used. For example, initially a film of nano-sized metal oxide
particles is formed on a substrate, and then a polylinker solution is
sprayed on the film. Alternatively, a method in which nano-sized metal
oxide particles are dispersed in a polylinker solution, and the
dispersion is applied on a substrate can be used. In this regard, micro
fluidizing methods, attriting methods, and ball milling can be used for
dispersing nano-sized metal oxide particles in a solvent. Further, a
method in which initially a polylinker solution is applied on a
substrate, and then a film of nano-sized metal oxide particles is formed
thereon can also be used.

[0205] By using the method in which nano-sized metal oxide particles are
dispersed in a polylinker solution, a film of nano-sized metal oxide
particles connected with each other can be prepared by one step. Specific
examples of the method for applying such a dispersion include printing
methods such as screen printing and gravure printing. In the method in
which initially a polylinker solution is applied on a substrate, and then
a film of nano-sized metal oxide particles is formed thereon, the
concentration of the polylinker in the solution is controlled such that
the coated polylinker layer has a predetermined thickness. In addition,
before forming a film of nano-sized metal oxide particles on the coated
polylinker layer, part (excess) of the solvent may be removed from the
coated polylinker layer.

[0206] The formula of the nano-sized particles is not limited to MxOy. For
example, sulfides, selenides, and tellurides of metals such as Ti, Zr,
La, Nb, Sn, Ta, Tb, Mo, and W can also be used Suitable materials for use
as the nano-sized particles include TiO2, SrTiO3, CaTiO3,
ZrO2, WO3, La2O3, Nb2O3, SnO2, sodium
titanate, and potassium niobate.

[0207] The polylinker for use in the present invention can have one or
more kinds of reactive groups. In the example mentioned above, the
polylinker has one kind of reactive group, OR. However, the polylinker
can have plural kinds of reactive groups such as OR, OR', and OR'',
wherein each of R, R' and R'' represents a hydrogen atom, an alkyl group,
an alkenyl group, an aromatic group, or an acyl group. Alternatively, the
reactive group OR can be replaced with a halogen atom. For example, the
polylinker can have a polymer unit having a formula such as
--[O-M(OR)i(OR')j-]-, and --[O-M(OR)i(OR')j(OR'')k-]-, wherein each of i,
j, and k is a positive integer.

[0208] In the present invention, a method in which initially a polylinker
solution is applied on a substrate, and then nano-sided particles are
applied thereon to form an electroconductive oxide layer can be used.
Specifically, when titanium dioxide is used for the nano-sided particles,
initially a polylinker solution including poly(n-butyltitanate) is
dissolved in n-butanol, and the solution is applied on a substrate. In
this regard, the concentration of the polylinker in the solution is
controlled such that the coated polylinker layer has a predetermined
thickness. Next, a film of nano-sized titanium dioxide is formed on the
polylinker layer. In this case, a hydroxyl group on the surface of the
titanium oxide particles is reacted with a butoxy group (or another
alkoxyl group) of poly(n-butyltitanate), thereby connecting the
nano-sized particles with each other and the substrate.

[0209] The flexible and light transmissive substrate preferably includes a
polymer. Specific examples thereof include PET, polyimide, PEN,
polymer-like hydrocarbons, cellulose compounds, and combinations of these
materials. In addition, the substrate can include a material on which the
solar cell can be prepared by a method such as roll-to-roll methods and
web methods. The substrate may be colored, but is preferably colorless.
The substrate has one or more flat surfaces, but can have a surface which
is not substantially flat. For example, the substrate can have a curved
or stepped surface, for example, to form a Frensnel lens. In addition,
the surface of the substrate may be subjected to patterning.

[0210] In the photoelectric converter of this disclosure, an
electroconductive material layer can be formed on one or both of the
surfaces of the substrate. Suitable materials for use as the
electroconductive material include materials having high light
transmittance such as ITO, fluorine-doped oxides, tin oxide, and zinc
oxide. The thickness of the electroconductive material layer is
preferably from about 100 nm to about 500 nm, and more preferably from
about 150 nm to about 300 nm. In addition, a wire or conductor can be
connected with the electroconductive material layer to electrically
connect the solar cell with an external load.

[0211] The nano-sized particles connected with each other can include one
or more nano-sized particulate metal oxides, which preferably have an
average particle diameter of from about 2 nm to about 100 nm, more
preferably from about 10 nm to about 40 nm, and even more preferably
about 20 nm.

[0212] Various kinds of photosensitizers can be applied to nano-sized
particles so that the nano-sized particles are connected with each other.
Such photosensitizers assist to convert incident light to electricity,
thereby enhancing the solar cell effect. Such photosensitizers absorb
incident light, and cause electronic excitation. Due to the energy of the
excited electrons, the electrons are transferred from the excited level
of the sensitizers to the conduction band of the nano-sized particles,
thereby efficiently causing charge separation resulting in production of
the solar cell effect. The electrons in the conduction band of the
nano-sized particles are used for driving an external load electrically
connected with the solar cell.

[0213] The photosensitizer is chemically or physically adsorbed on a
surface or the entire surface of the nano-sized particles connected with
each other. A suitable photosensitizer is selected in consideration of
the photon absorbing ability, the free electron generating ability in the
conduction band of the nano-sized particles connected with each other, an
ability to form a complex with the nano-sized particles, and an ability
to be adsorbed on the nano-sized particles. Suitable materials for use as
the photosensitizer include materials, which have a functional group such
as a carboxyl group and a hydroxyl group and which can form a chelate,
for example, with the Ti(VI) site of TiO2. Specific examples thereof
include anthocyanin, porphyrin, phthalocyanine, merocyanine, cyanine,
squarate, eosin,
cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4-dicarboxylato)ruthenium
(II) (i.e., N3), tris(isthiocyanato)ruthenium
(II)-2,2';6',2''-terpyridyl-4,4',4''-tricarboxylic acid,
cis-bis(isocyanate)bis(2,2'-bipyridyl-4,4-dicarboxylato)ruthenium
(II)bis-tetrabutylamonium,
cis-bis(isocyanate)bis(2,2'-bipyridyl-4,4-dicarboxylato)ruthenium
(II)dichloride, and the like. These materials can be available from
SOLARONIX SA.

[0214] The portion of the solar cell including a charge transport material
is formed by forming a charge transport material layer in the solar cell,
and/or by dispersing a charge transport material in the nano-sized
particles for use in forming the nano-sized photosensitive particle
layer. Any known materials which can accelerate charge transport of from
a current source to the nano-sized photosensitive particle layer can be
used as the charge transport material. Suitable materials for use as the
charge transport material include solvent-based liquid electrolytes,
polymer electrolytes, solid electrolytes, n-type or p-type charge
transport materials (e.g., electroconductive polymers), and gel
electrolytes. These materials will be described below in detail.

[0215] Other materials can be used for the charge transport material. For
example, lithium salts having a formula LiX can be used, wherein X
represents iodide, bromide, chloride, perchlorate, thiocyanide,
trifluoromethylsulfonate, or hexafluorophosphate. The charge transport
material preferably includes a redox system such as organic redox systems
and/or inorganic redox systems. Specific examples of the redox system
include cerium(III)sulfide/cerium(IV), sodium bromide/bromine, lithium
iodide/iodine, Fe2+/Fe, Co2+/Co3+, and viologen, but are
not limited thereto. In addition, the electrolyte solution includes MiXj,
wherein each of i and j is a positive integer, X represents an anion, and
M represents Li, Cu, Ba, Zn, Ni, lanthanide, Co, Ca, Al, or Mg. Specific
examples of the group X (anion) include chloride, perchlorate,
thiocyanide, trifluoromethylsulfonate, or hexafluorophosphate.

[0216] The charge transport material preferably includes a polymer
electrolyte such as combinations of poly(vinylimidazolium halogenide) and
lithium iodide, and poly(vinylpyridinium salt). Alternatively, the charge
transport material includes a solid electrolyte such as lithium iodide,
pyridinium iodide, and substituted imidazolium iodide.

[0217] In addition, the charge transport material can include a polymer
electrolyte composition including a polymer (such as ion-conducting
polymer), a plasticizer, and a redox electrolyte (such as combinations of
an organic or inorganic iodide and iodine). The content of the polymer is
from about 5% by weight to about 100% by weight, preferably from 5% to
60%, more preferably 5% to 40%, and even more preferably from 5% to 20%.
The content of the plasticizer is from about 5% by weight to about 95% by
weight, preferably from 35% to 95%, more preferably 60% to 95%, and even
more preferably from 80% to 95%. The concentration of the redox
electrolyte is from about 0.05M to about 10M, wherein the concentration
of an organic or inorganic iodide is from 0.05M to 10M, preferably from
0.05M to 2M, and more preferably from 0.05M to 0.5M, and the
concentration of iodine is from 0.01M to 10M, preferably from 0.05M to
5M, more preferably from 0.05M to 2M, and even more preferably from 0.05M
to 1M. Specific examples of the ion-conducting polymer include
polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl
methacrylate (PMMA), polyether, and polyphenol. Specific examples of the
plasticizer include ethyl carbonate, propylene carbonate, mixtures of
carbonates, organic phosphates, butyrolactone, and dialkylphthalate.

[0218] The flexible solar cell of this disclosure can include a layer
having a catalytic activity, which is located between substrates. The
layer having a catalytic activity is electrically connected with a charge
transport material in the solar cell. The layer having a catalytic
activity includes ruthenium, osmium, cobalt, rhodium, iridium, nickel,
activated carbon, palladium, platinum, or a hole transport polymer (such
as poly(3,4-ethylenedioxythiophene) and polyaniline). More preferably,
the layer further includes a metal such as titanium to improve adhesion
of the layer to a substrate or a coated layer on a substrate. In this
regard, the metal (such as titanium) forms a layer having a thickness on
the order of about 10 Angstroms. Alternatively, the layer can include a
platinum layer having a thickness of from about 13 Angstroms to about 50
Angstroms, and preferably about 25 Angstroms.

[0219] When a layer of nano-sized photosensitive particles is formed, a
method in which a coating liquid including a polylinker solution and a
nano-sized particulate metal oxide is applied on a moving substrate sheet
can be used. The coating method is not particularly limited, and for
example, dip coating, extrusion coating, spray coating, screen printing,
and gravure printing can be used therefor. Alternatively, a method in
which initially a polylinker solution is applied on a moving substrate
sheet, and then a nano-sized particulate metal oxide is applied thereon
can also be used. Further, a method in which initially a polylinker
solution is applied on a moving substrate sheet, and then a nano-sized
particulate metal oxide dispersed in a solvent is applied thereon can
also be used. Furthermore, a method in which initially a nano-sized
particulate metal oxide (preferably dispersed in a solvent) is applied on
moving substrate sheet, and then a polylinker solution is applied thereon
can also be used.

[0220] After a photosensitive nano-matrix material is prepared on a
substrate, the substrate can be further subjected to a treatment.
Specifically, a charge transport material to accelerate charge transport
of from a current source to the photosensitive nano-sized particulate
material is applied thereon. Specific examples of the application method
include spray coating, roller coating, knife coating, and blade coating.
The charge transport material is typically prepared by using a solution
including an ion-conducting polymer, a plastiizer, and a mixture of an
iodide and iodine. The polymer imparts mechanical stability or
dimensional stability to the layer, the plasticizer contributes to
gel/liquid phase transition temperature, and the mixture of an iodide and
iodine serves as a redox electrolyte.

[0221] Next, the first and second insulating layers 24 and 25 will be
described.

[0222] The material of the first and second insulating layers 24 and 25 is
not particularly limited as long as the material is porous. Suitable
materials for use in the insulating layers, include materials having a
good combination of insulating property, durability and film formability
such as materials including ZnS. ZnS has an advantage such that a layer
can be rapidly formed by sputtering without damaging an electron
transport layer. Specific examples of the materials including ZnS include
ZnS--SiO2, ZnS--SiC, ZnS--Si, and ZnS--Ge. The content of ZnS in the
materials including ZnS is preferably from about 50% by mol to about 90%
by mol so that the ZnS maintains crystallinity in the resultant
insulating layer. Among these materials, ZnS--SiO2 (8/2),
ZnS--SiO2 (7/3), ZnS, ZnS--ZnO--In2O3--Ga2O3
(60/23/10/7) are more preferable.

[0223] By using such materials for the insulating layers, the insulating
layers have good insulating properties even when the layers are thin.
Therefore, even when multiple insulating layers are overlaid,
deterioration of the strength of the layers can be prevented (i.e.,
peeling of the layers can be avoided).

[0224] A porous insulating layer can be prepared, for example, by forming
an insulating film consisting of a particulate material. Specifically,
when a ZnS insulating layer is prepared by sputtering, a porous
insulating layer can be prepared, for example, by forming the ZnS
insulating layer on a granular undercoat layer. In this case, metal
oxides can be used for the granular undercoat layer, but insulating
particles such as silica and alumina can be preferably used.

[0225] By forming such a porous insulating layer, the electrolyte in the
charge transport layer can penetrates the insulating layer.

[0226] The thickness of the insulating layer is preferably from 20 nm to
500 nm, and more preferably from 50 nm to 150 nm. When the insulating
layer is too thin, the insulating layer has insufficient insulating
property. In contrast, when the insulating layer is too thick, the
manufacturing costs increase.

[0227] Next, the intermediate electrodes 22 and 23 will be described.

[0228] The materials mentioned above for use in the electron collecting
electrode 3 can also be used for the first and second intermediate
electrodes 22 and 23. When the material used for the intermediate
electrodes has good strength and sealing ability, the electrodes do not
necessarily have a substrate.

[0229] Specific examples of the materials for use in the intermediate
electrodes 22 and 23 include metals such as platinum, gold, silver,
copper, and aluminum, carbon compounds such as graphite, fullerene, and
carbon nanotube, electroconductive metal oxides such as ITO and FTO, and
electroconductive polymers such as polythiophene, and polyaniline. These
materials can be used alone or in combination.

[0230] The thickness of the intermediate electrodes is not particularly
limited.

[0231] The intermediate electrodes have voids in which a hole transport
material is contained. FIG. 3 is a photograph of a surface of an
intermediate electrode taken by an optical microscope. Specifically, FIG.
3 is a photograph of a void present on a surface of an intermediate
electrode. The void has a size (width) of from 0.5 μm to 500 μm.
However, there are voids in the intermediate electrode, which cannot be
observed by an optical microscope. The size of such small voids is from
50 nm to 500 nm.

[0232] The intermediate electrodes having voids can transmit holes and
light. Since light proceeds while scattering in a TiO2 layer (i.e.,
light cannot proceed straight), the transmittance cannot be measured.

[0233] Hereinafter, the photoelectric converter of this disclosure will be
described by reference to examples of DSSC including a nano-sized
particulate TiO2. The nano-sized particulate material is not limited
to TiO2, and for example, SrTiO3, CaTiO3, ZrO2,
La2O3, Nb2O5, sodium titanate, potassium niobate, and
the like can also be used. In addition, the photoelectric converter of
this disclosure is not limited to DSSC. Therefore, metal oxides and
semiconductor coating, in which nano-sized particles are connected with
each other, can also be applied to the photoelectric converter so that
the resultant photoelectric converter can be used for devices other than
DSSC.

[0234] The photoelectric converter of this disclosure can be used for
solar cells, power supplies using a solar cell, devices using such a
power supply. For example, the photoelectric converter of this disclosure
can be used for a solar cell for use in electronic calculators, and
watches. In addition, the photoelectric converter of this disclosure can
be preferably used for a power supply for use in cellular phones,
electronic organizers, and electronic papers. Further, the photoelectric
converter of this disclosure can also be used for an auxiliary power
supply to prolong the usage time of a rechargeable battery or a battery
in electric devices.

[0235] Having generally described this invention, further understanding
can be obtained by reference to certain specific examples which are
provided herein for the purpose of illustration only and are not intended
to be limiting. In the descriptions in the following examples, the
numbers represent weight ratios in parts, unless otherwise specified.

EXAMPLES

Example 1

[0236] A DSSC was prepared as follows.

[0237] Initially, a glass plate with a thickness of 1 mm, a surface of
which was coated with a material SnO2:F serving as the first
electrode, was provided. When the resistance between two terminals of the
first electrode was measured to determine the sheet resistance thereof,
the sheet resistance was about 20Ω.

[0238] Next, a nano-sized titanium oxide dispersion (SP210 from Showa
Titanium Co., Ltd.) was applied on the first electrode by spin coating,
followed by annealing for 15 minutes at 120° C. Thus, a titanium
oxide particle layer serving as an electron transport layer was prepared.

[0239] Further, an ethanol solution of a dye D131 having the
below-mentioned formula (3) was applied on the titanium oxide particle
layer by spin coating, followed by annealing for 10 minutes at
120° C. Thus, a first photoelectric conversion layer including the
titanium oxide particle layer and the dye D131 was prepared.

##STR00003##

[0240] Next, a layer of ZnS--SiO2 (8/2 by mol) having a thickness of
from 25 to 150 nm (in this case, about 34 nm) was prepared on the first
photoelectric conversion layer by sputtering. Thus, an inorganic
insulating layer was formed.

[0241] Further, an ITO layer having a thickness of about 100 nm was formed
on an area (with a size of 10 mm×20 mm) of the surface of the
inorganic insulating layer, resulting in formation of a second electrode
(i.e., an electroconductive material layer). The sheet resistance of the
second electrode, which is determined by measuring resistance between two
terminals set on the second electrode, was about 10Ω to about
200Ω.

[0242] Next, a nano-sized titanium oxide dispersion (SP210 from Showa
Titanium Co., Ltd.) was applied on the second electrode by spin coating,
followed by annealing for 15 minutes at 120° C. Thus, a titanium
oxide particle layer serving as an electron transport layer was formed on
the second electrode.

[0243] Further, a coating liquid in which a 1% by weight dye solution
prepared by dissolving a dye Y7-19 having the below-mentioned formula (4)
in 2,2,3,3-tetrafluoropropanol was mixed with the titanium oxide
dispersion SP210 mentioned above in a weight ratio of 2.4/4 was applied
on the titanium oxide particle layer by spin coating. Thus, a second
photoelectric conversion layer including titanium oxide particles and the
sensitizing dye was prepared.

##STR00004##

[0244] Next, an opposite electrode was prepared.

[0245] A transparent electroconductive layer of tin oxide was formed on
one surface of a glass substrate of 10 mm×20 mm. In addition, a
thermosetting electroconductive carbon ink CH10 from Jujo Chemical Co.,
Ltd. and 2-ethoxyethyl acetate were mixed in a ratio of 1:0.25 to prepare
a coating liquid. The coating liquid was applied on the above-prepared
transparent electroconductive layer by spin coating, followed by
annealing for 15 minutes at 120° C. Thus, an opposite electrode
was prepared. The opposite electrode was adhered to the second
photoelectric conversion layer.

[0246] The following components were mixed to prepare a solution of an
electrolyte composition (hole transport material).

[0247] The thus prepared electrolyte composition solution was injected
into the device sandwiched by the substrates from an inlet thereof
(located in the vicinity of the first electrode) using a pump while
depressurizing to remove air bubbles from the device, and the inlet was
sealed with an ionomer film, an acrylic resin and a glass plate. Thus, a
dye sensitized photoelectric converter (i.e., DSSC) was prepared.

[0248] The DSSC was evaluated using a sunlight simulator at a light
intensity of 1,000 W/m2. The evaluation items were as follows.

TABLE-US-00002
TABLE 1
Sample Voc (V) Jsc (mA/cm2) ff η (%)
Tandem (upper 0.603 0.408 0.524 0.129
and lower layers)
Tandem (only 0.508 0.167 0.436 0.037
upper layer)
In this DSSC, parallel connection was made. Although the upper layer has a
relatively small average short-circuit current Jsc of 0.167, the tandem
(upper and lower layers) can have a large average short-circuit current
Jsc (0.408).

[0250] It can be understood from FIGS. 4 and 5 that the dyes included in
the upper and lower layers function independently.

Example 2

[0251] A glass plate with a thickness of 1 mm coated with SnO2:F
(first electrode) was provided.

[0252] Next, a nano-sized titanium oxide dispersion (T20 from SOLARONIX
SA) was applied on the first electrode by a printing method, followed by
annealing for 30 minutes at 550° C. Thus, a titanium oxide
particle layer with a thickness of 9 μm was prepared.

[0253] In addition, a solution SNOW LATEX MIBK-SZC from Nissan Chemical
industries Ltd., which includes silica as a solid component, methyl
isobutyl ketone, and methanol at a weight ratio of 45%, 50% and 5%, was
applied on the above-prepared titanium oxide particle layer by spin
coating at a revolution of 2500 rpm.

[0254] Further, the following components were mixed to prepare a coating
liquid.

[0255] The coating liquid was applied on the above-prepared titanium oxide
particle layer by spin coating at a revolution of 2,500 rpm.

[0256] Further, a ZnS/SiO2 layer with a thickness of 34 nm was formed
on the above-prepared layer by sputtering, and an ITO layer with a
thickness of 77 nm was formed thereon by sputtering.

[0257] Furthermore, the nano-sized titanium oxide dispersion (T20 from
SOLARONIX SA) was applied on the layer by a printing method, followed by
annealing for 30 minutes at 550° C. Thus, a titanium oxide
particle layer with a thickness of 3.1 μm was prepared.

[0258] The thus prepared cell was dipped into an ethanol solution of a dye
having the above-mentioned formula (I) for 1 hour at 60° C.

[0259] Thereafter, the cell was washed with ethanol to remove excessive
dye therefrom, followed by annealing for 3 minutes at 120° C. to
remove the solvent therefrom.

[0260] The following components were mixed to prepare a solution of an
electrolyte composition (hole transport material).

[0261] The thus prepared electrolyte composition solution was injected
into the device sandwiched by the substrates from an inlet thereof using
a pump while depressurizing to remove air bubbles from the device, and
the inlet was sealed with an ionomer film, an acrylic resin and a glass
plate. Thus, a dye (D102) sensitized photoelectric converter (i.e., DSSC)
of Example 2 was prepared.

[0262] The DSSC of Example 2 was evaluated by the method described above
in Example 1.

[0264] A glass plate with a thickness of 1 mm coated with SnO2:F
(first electrode) was provided.

[0265] A nano-sized titanium oxide dispersion was coated on the first
electrode by spin coating to prepare a dense titanium oxide layer
thereon.

[0266] Next, a nano-sized titanium oxide dispersion (T20 from SOLARONIX
SA) was applied on the dense titanium oxide layer by a printing method,
followed by annealing for 30 minutes at 550° C. Thus, a titanium
oxide particle layer with a thickness of 9 μm was prepared.

[0267] In addition, a solution SNOW LATEX MIBK-SZC from Nissan Chemical
industries Ltd., which includes silica as a solid component, methyl
isobutyl ketone, and methanol at a weight ratio of 45%, 50% and 5%, was
applied on the above-prepared titanium oxide particle layer by spin
coating at a revolution of 2,500 rpm.

[0268] Further, the following components were mixed to prepare a coating
liquid.

[0275] The thus prepared electrolyte composition solution was injected
into the device sandwiched by the substrates from an inlet thereof using
a pump while depressurizing to remove air bubbles from the device, and
the inlet was sealed with an ionomer film, an acrylic resin and a glass
plate. Thus, a dye (D102) sensitized photoelectric converter (i.e., DSSC)
of Example 3 was prepared.

[0276] The DSSC of Example 3 was also evaluated by the method described
above in Example 1. As a result, the DSSC had substantially the same
properties as the DSSC of Example 2.

Example 4

[0277] A glass plate with a thickness of 1 mm coated with SnO2:F
(first electrode) was prepared.

[0278] Next, a titanium oxide paste, which was prepared as mentioned
below, was applied on the first electrode to prepare a titanium oxide
layer.

[0279] The titanium oxide paste was prepared as follows. Specifically, 125
ml of titanium isopropoxide was dropped into 750 ml of a 0.1M aqueous
solution of nitric acid at room temperature while agitating the mixture.
Thereafter the mixture was heated to 80° C. in a chamber while
agitated. As a result, a semi-transparent clouded sol was obtained.

[0280] After the sol was cooled to room temperature, the sol was filtered
with a glass filter, and the filtered sol was mixed with a solvent to
increase the volume to 700 ml.

[0281] The sol was heated for 12 hours at 220° C. in an autoclave
to perform a hydrothermal reaction, followed by a supersonic dispersing
treatment for 1 hour.

[0282] Further, the sol was condensed at 40° C. using an evaporator
so as to have a TiO2 content of 20% by weight.

[0283] The condensed sol was mixed with polyethylene glycol in an amount
of 20% by weight based on the weight of the titanium oxide included in
the sol, and anatase-form titanium oxide having a particle diameter of
200 nm in an amount of 30% by weight based on the weight of the titanium
oxide, and the mixture was agitated by an agitating deaerator. Thus, a
titanium oxide paste dispersion was prepared.

[0284] The procedure for preparation and evaluation of the DSSC of Example
2 was repeated except that the first particulate electron transport layer
was prepared using the titanium oxide paste dispersion. As a result, the
DSSC had substantially the same properties as the DSSC of Example 2.

Example 5

[0285] The procedure for preparation and evaluation of the DSSC of Example
1 was repeated except that the titanium oxide was replaced with zinc
oxide. The resultant solar cell had a photoelectric conversion efficiency
of 0.5%.

Example 6

[0286] The procedure for preparation and evaluation of the DSSC of Example
1 was repeated except that the titanium oxide was replaced with tin
oxide. The resultant solar cell had a photoelectric conversion efficiency
of 0.31%.

Example 7

[0287] The procedure for preparation and evaluation of the DSSC of Example
1 was repeated except that the dip coating method used for applying the
dye solution was replaced with a method in which the dye solution is set
at an edge of the electrode so that the dye solution penetrated the cell.
The evaluation results of the solar cell are shown in Table 3 below.

[0288] A glass plate with a thickness of 1 mm coated with SnO2:F
(first electrode) was provided.

[0289] Next, a nano-sized titanium oxide dispersion (T20 from SOLARONIX
SA) was applied on the first electrode by a printing method, followed by
annealing for 30 minutes at 550° C. Thus, a titanium oxide
particle layer with a thickness of 9 μm was prepared.

[0290] In addition, a solution SNOW LATEX MIBK-SZC from Nissan Chemical
industries Ltd., which includes silica as a solid component, methyl
isobutyl ketone, and methanol at a weight ratio of 45%, 50% and 5%, was
applied on the above-prepared titanium oxide particle layer by spin
coating at a revolution of 2,500 rpm.

[0291] Further, the following components were mixed to prepare a coating
liquid.

[0292] The coating liquid was applied on the above-prepared titanium oxide
particle layer by spin coating at a revolution of 2,500 rpm.

[0293] Further, a ZnS/SiO2 layer with a thickness of 34 nm was formed
on the above-prepared layer by sputtering, and an ITO layer with a
thickness of 77 nm was formed thereon by sputtering.

[0294] Furthermore, the nano-sized titanium oxide dispersion (T20 from
SOLARONIX SA) was applied on the layer by a printing method, followed by
annealing for 30 minutes at 550° C.

[0295] Thus, a titanium oxide particle layer with a thickness of 3.1 μm
was prepared.

[0296] In addition, a solution SNOW LATEX MIBK-SZC from Nissan Chemical
industries Ltd., which includes silica as a solid component, methyl
isobutyl ketone, and methanol at a weight ratio of 45%, 50% and 5%, was
applied on the above-prepared titanium oxide particle layer by spin
coating at a revolution of 2,500 rpm.

[0297] Further, the following components were mixed to prepare a coating
liquid.

[0298] The coating liquid was applied on the above-prepared titanium oxide
particle layer by spin coating at a revolution of 2,500 rpm.

[0299] Further, a ZnS/SiO2 layer with a thickness of 34 nm was formed
on the above-prepared layer by sputtering, and an ITO layer with a
thickness of 77 nm was formed thereon by sputtering.

[0300] Furthermore, the nano-sized titanium oxide dispersion (T20 from
SOLARONIX SA) was applied on the layer by a printing method, followed by
annealing for 30 minutes at 550° C. Thus, a titanium oxide
particle layer with a thickness of 3.1 μm was prepared.

[0301] The thus prepared cell was dipped into an ethanol solution of a dye
having the above-mentioned formula (I) for 1 hour at 60° C.

[0302] Thereafter, the cell was washed with ethanol to remove excessive
dye therefrom, followed by annealing for 3 minutes at 120° C. to
remove the solvent therefrom.

[0303] The following components were mixed to prepare a solution of an
electrolyte composition (hole transport material).

[0304] The thus prepared electrolyte composition solution was injected
into the device sandwiched by the substrates from an inlet thereof using
a pump while depressurizing to remove air bubbles from the device, and
the inlet was sealed with an ionomer film, an acrylic resin and a glass
plate. Thus, a dye sensitized photoelectric converter (i.e., DSSC) of
Example 8 was prepared.

[0305] The DSSC of Example 8 was evaluated by the method described above
in Example 1. As a result, it was confirmed that the DSSC can perform
photoelectric conversion.

Example 9

[0306] Initially, a glass plate with a thickness of 1 mm, on a surface of
which was coated with a material SnO2:F serving as the first
electrode, was provided. When the resistance between two terminals of the
electrode was measured to determine the sheet resistance thereof, the
sheet resistance was about 20Ω.

[0307] Next, a nano-sized titanium oxide dispersion (SP210 from Showa
Titanium Co., Ltd.) was applied on the first electrode by spin coating,
followed by annealing for 15 minutes at 120° C. Thus, a titanium
oxide particle layer serving as an electron transport layer was prepared.

[0308] In addition, an ethanol solution of a dye D131 having the
above-mentioned formula (3) was applied on the titanium oxide particle
layer by spin coating, followed by annealing for 10 minutes at
120° C. Thus, a first photoelectric conversion layer including
titanium oxide particles and the dye D131 was prepared.

[0309] Further, a ZnS/SiO2 (8:2) layer with a thickness of from 25 nm
to 150 nm (in this case, 34 nm) was formed on the above-prepared layer by
sputtering to prepare an inorganic insulating layer.

[0310] Furthermore, an ITO layer having a thickness of about 100 nm was
formed on an area (with a size of 10 mm×20 mm) of the surface of
the inorganic insulating layer, resulting in formation of a second
electrode (i.e., an electroconductive material layer. The sheet
resistance of the second electrode, which is determined by measuring
resistance between two terminals set on the second electrode, was about
10Ω to about 200Ω.

[0311] Next, a nano-sized titanium oxide dispersion (SP210 from Showa
Titanium Co., Ltd.) was applied on the second electrode by spin coating,
followed by annealing for 15 minutes at 120° C. Thus, a titanium
oxide particle layer serving as an electron transport layer was formed on
the second electrode.

[0312] In addition, a coating liquid in which a 1% by weight dye solution
prepared by dissolving a dye Y7-19 having the above-mentioned formula (4)
in 2,2,3,3-tetrafluoropropanol was mixed with the titanium oxide
dispersion SP210 mentioned above in a weight ratio of 2.4/4 was applied
on the titanium oxide particle layer by spin coating. Thus, a second
photoelectric conversion layer including titanium oxide particles and the
sensitizing dye was prepared.

[0313] Further, a ZnS/SiO2 (8:2) layer with a thickness of from 25 nm
to 150 nm (in this case, 34 nm) was formed on the above-prepared layer by
sputtering to prepare an inorganic insulating layer.

[0314] Furthermore, an ITO layer having a thickness of about 100 nm was
formed on an area (with a size of 10 mm×20 mm) of the surface of
the inorganic insulating layer, resulting in formation of a third
electrode (i.e., an electroconductive material layer). The sheet
resistance of the third electrode, which is determined by measuring
resistance between two terminals set on the third electrode, was about
10Ω to about 200Ω.

[0315] Next, a nano-sized titanium oxide dispersion (SP210 from Showa
Titanium Co., Ltd.) was applied on the third electrode by spin coating,
followed by annealing for 15 minutes at 120° C. Thus, a titanium
oxide particle layer serving as an electron transport layer was formed on
the third electrode.

[0316] In addition, a coating liquid in which a 1% by weight dye solution
prepared by dissolving a dye D102 having the above-mentioned formula (I)
in 2,2,3,3-tetrafluoropropanol was mixed with the titanium oxide
dispersion SP210 mentioned above in a weight ratio of 2.4/4 was applied
on the titanium oxide particle layer by spin coating. Thus, a third
photoelectric conversion layer including titanium oxide particles and the
sensitizing dye was prepared.

[0317] The opposite electrode was prepared as follows.

[0318] A transparent electroconductive layer of tin oxide was formed on
one surface of a glass substrate of 10 mm×20 mm. In addition, a
thermosetting electroconductive carbon ink CH10 from Jujo Chemical Co.,
Ltd. and 2-ethoxyethyl acetate were mixed in a ratio of 1:0.25 to prepare
a coating liquid. The coating liquid was applied on the above-prepared
transparent electroconductive layer by spin coating, followed by
annealing for 15 minutes at 120° C. Thus, an opposite electrode
was prepared.

[0319] The following components were mixed to prepare a solution of an
electrolyte composition (hole transport material).

[0320] The thus prepared electrolyte composition solution was injected
into the device sandwiched by the substrates from an inlet thereof using
a pump while depressurizing to remove air bubbles from the device, and
the inlet was sealed with an ionomer film, an acrylic resin and a glass
plate. Thus, a dye sensitized photoelectric converter (i.e., DSSC) was
prepared.

[0321] This DSSC has a configuration such that a layer of the DSSC located
closer to the substrate absorbs light having a shorter wavelength.

[0322] The DSSC was also evaluated by the method described in Example 1.
As a result, it was confirmed that the DSSC of Example 9 has a
photoelectric conversion ability.

Comparative Example 1

[0323] The procedure for preparation and evaluation of the DSSC in Example
2 was repeated except that the DSSC is a single-layer solar cell in which
the single titanium oxide layer has a thickness of 9 μm whereas the
DSSC of Example 2 is a tandem solar cell. In this regard, a modified
version of the DSSC of Example 2, in which the thickness (9 μm) of the
first titanium oxide particle layer was changed to 6.4 μm so that the
total thickness of the titanium oxide layers becomes about 9 μm, was
also prepared for comparison. The evaluation results of the DSSC of
Comparative Example 1 are shown in Table 4 below.

[0324] Additional modifications and variations of the present invention
are possible in light of the above teachings. It is therefore to be
understood that within the scope of the appended claims the invention may
be practiced other than as specifically described herein.